Flow battery systems

ABSTRACT

Embodiments of the invention generally provide for flow battery cells and systems containing a plurality of flow battery cells, and methods for improving metal plating within the flow battery cell, such as by flowing and exposing the catholyte to various types of cathodes. In one embodiment, a flow battery cell is provided which includes a cathodic half cell and an anodic half cell separated by an electrolyte membrane, wherein the cathodic half cell contains a plurality of cathodic wires extending perpendicular or substantially perpendicular to and within the catholyte pathway and in contact with the catholyte, and each of the cathodic wires extends parallel or substantially parallel to each other. In some examples, the plurality of cathodic wires may have at least two arrays of cathodic wires, each array contains at least one row of cathodic wires, and each row extends along the catholyte pathway.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention generally relate to electrochemical cellsand more particular to flow battery cells and systems.

2. Description of the Related Art

Flow batteries containing electrochemical cells have been around forseveral decades and are used to store electrical energy. Although avariety of flow batteries exist in the art, a couple of known types offlow batteries include the zinc-ferrocyanide battery and thezinc-bromide battery. When these types of battery cells are charged, ametal (e.g., zinc) is plated onto a planar electrode within the batterycell. For an efficient battery cell, the metal should be plated at anacceptable rate, uniformity, volume, and morphology. An important aspectwith flow batteries is that all or substantially all of the metal platedonto the planar electrode is available for deplating during thedischarge of the battery cell. For example, metal plated with amorphology that has poor adhesion may fall off the planar electrodebefore the electrical discharge and the energy stored while plating thismetal would be lost.

Furthermore, a current density distribution created during plating(e.g., metal thickness uniformity) that is different than the currentdensity obtained during the discharge leads to non-uniform metalbuild-up over many charge/discharge cycles. As a result, the metal willbe depleted down to the electrode in some regions and not in others,possibly leading to gas evolution, higher cell potentials, and/orreduced battery efficiency. Flaked or deplated metal particles whichaccumulate in the battery cell may block the electrolyte flow paths orchannels, enter and contaminate the electrolyte membrane, or cause otherproblematic issues—if left without intervention (e.g., removal of theflaked metal). Similarly, metal plated onto certain portions of theelectrode and not subsequently deplated may build up over many chargecycles of the battery causing issues such as flow blockage, shorting, ormembrane damage.

Additionally, the compact nature of a typical flow battery cellgenerally creates challenges to obtaining optimal plating performance.The typical flow battery cell often has electrodes with a large surfacearea separated by small gaps to minimize cell ohmic resistance (forhigher battery efficiency) and to keep a plurality of flow battery cellspacked within a dense array. As a result, the flow path for theelectrolyte is restricted to a narrow channel which makes it difficultto provide a uniform, high rate of ion replenishment across a largesurface area electrode. Also, ion replenishment can be increased withhigher electrolyte flow rates, but it is desirable to keep pumping flowrates and pressure losses (pump energy requirements) as small aspossible to keep the battery efficiency.

Therefore, there is a need for a flow battery cell having an improvedion replenishment (e.g., mass transfer) to the electrode surface toprovide metal plating at increased rates, volumes, uniformity, andmorphology over a traditional flow battery having a planar electrode.

SUMMARY OF THE INVENTION

Embodiments of the invention generally provide for flow battery cells,flow battery systems containing a plurality of the flow battery cells,and methods for improving metal plating within the flow battery cell,such as by flowing and exposing the catholyte to various types ofcathodes. Each flow battery cell generally contains a cathodic half celland an anodic half cell separated by an electrolyte membrane which isdisposed between the cathodic half cell and the anodic half cell and influid communication with a catholyte and an anolyte. The cathodic halfcell contains a cathode in conductive contact with the catholyte flowingalong a catholyte pathway which extends between a catholyte inlet and acatholyte outlet disposed on opposite sides of the cathodic half cell.The anodic half cell contains an anode in conductive contact with theanolyte flowing along an anolyte pathway which extends between ananolyte inlet and an anolyte outlet disposed on opposite sides of theanodic half cell. A cathodic contact is disposed outside of the cathodichalf cell and is electrically connected with the cathode, and an anodiccontact is disposed outside of the anodic half cell and is electricallyconnected with the anode.

In one embodiment, a flow battery cell is provided which includes acathodic half cell containing a catholyte, a catholyte inlet, acatholyte outlet, a catholyte pathway extending between the catholyteinlet and outlet and within the cathodic half cell, and a cathodecontaining a plurality of cathodic wires extending perpendicular orsubstantially perpendicular to and within the catholyte pathway and incontact with the catholyte, and each of the cathodic wires extendsparallel or substantially parallel to each other. In some embodiments,the plurality of cathodic wires may have at least two arrays of cathodicwires, each array contains at least one row of cathodic wires, and eachrow extends along the catholyte pathway. In some examples, the pluralityof cathodic wires may have 2, 3, 4, or more rows of cathodic wires. Theplurality of cathodic wires may contain a first array of cathodic wireshaving energized cathodic wires and a second array of cathodic wireshaving non-energized cathodic wires during charge/discharge cycles ofthe flow battery. In some examples, the first array of cathodic wiresmay contain at least two rows of energized cathodic wires and the secondarray of cathodic wires contains at least two rows of non-energizedcathodic wires. In some configurations during charge/discharge cycles,the first array of cathodic wires may be disposed between the secondarray of cathodic wires and the electrolyte membrane, or alternatively,the second array of cathodic wires may be disposed between the firstarray of cathodic wires and the electrolyte membrane.

The cathodic wires are generally spaced a predetermined distance fromeach other within each row of cathodic wires. In many examples, thepredetermined distance is equal to or substantially equal to thecircumference of the cathodic wire. The cathodic wires may containcadmium or a cadmium alloy. The cathodic wires may be solid cadmiumwires or may be cadmium plated metallic wires, such as steel orstainless steel plated or coated with cadmium or a cadmium alloy. Thecathodic wires may have a diameter within a range from about 0.001 inchto about 0.1 inch, such as, from about 0.005 inch to about 0.05 inch, orsuch as, from about 0.01 inch to about 0.04 inch, or such as, from about0.02 inch to about 0.03 inch, for example, about 0.012 inch, 0.024 inchor 0.036 inch. The cathodic wires may have a length within a range fromabout 5 cm to about 300 cm, for example, from about 10 cm to about 50 cmor from about 20 cm to about 200 cm.

In many embodiments described herein, the cathodic wires are disposedperpendicular to the flow path of the electrolyte (e.g., catholyte)which provides many performance improvements for the flow battery cells.The cathodic wires generally produce more uniform metal plating whencompared to traditional planar electrodes. The flow battery systemgenerally has a higher cell current density while keeping the currentdensity on the cathodic wires reasonable (e.g., a low fraction of thelimiting current)—which in turn leads to a higher battery charge raterelative to a traditional battery. The flow battery system containing aplurality of cathodic wires generally has a larger metal storagecapacity leading to larger discharge times at a given current density,relative to traditional flow batteries. The sequential plating ofvarious arrays of cathodic wires helps to achieve longer discharge timesfor the flow battery system, as well as to provide in-situ electrodemaintenance to avoid downtime for electrode reconditioning—as comparedto a traditional planar electrode. For example, when deplating off onearray of cathodic wires, another array of cathodic wires may have asmall trickle discharge to insure complete or near complete removal ofthe plated metal. The cathodic wires provide plating and deplating rateswhich generally are more uniform and yield good performance over manycharge/discharge cycles—as compared to a traditional planar electrode.The cathodic wires yield a large surface area with a relative low volumeof metal contained therein. The large surface area of the cathodic wirestypically provides lower cell voltage drop and higher cell efficiency—ascompared to a traditional planar electrode. In some examples, thesurfaces of the cathodic wires contain cadmium, such as a solid cadmiumwire, a cadmium coated steel wire, or the like and the catholytecontains metal ions (e.g., zinc ions) which are electrochemicallyreduced and plated onto the cathodic wires as a metal film (e.g.,metallic zinc) during a charge cycle.

The flow battery cell further has an anode in fluid communication withan anodic half cell containing an anolyte, an anolyte inlet and outlet,and an anolyte pathway extending between the anolyte inlet and outletwithin the anodic half cell. The flow battery cell also contains acathodic contact electrically connected with the cathodic wires anddisposed outside of the cathodic half cell, and an anodic contactelectrically connected with the anode and disposed outside of the anodichalf cell. The anode may be a planar anode which contains iron, nickel,chromium, steel, stainless steel, alloys thereof, or combinationsthereof. In many embodiments, since the anodic half-cell reaction is aredox reaction, a porous electrode with a large surface area may bebeneficially included within the flow battery cell. Examples of porouselectrode material include nickel foam or graphite foam. The electrolytemembrane may contain a polymeric material and have a thickness within arange from about 0.005 mm to about 0.5 mm.

In another embodiment, a flow battery cell is provided which includes acathodic half cell containing a planar cathode, a catholyte, a catholyteinlet, a catholyte outlet, a catholyte pathway extending between thecatholyte inlet and outlet and within the cathodic half cell, and anopen block flow screen within the catholyte pathway. The open block flowscreen contains a plurality of blocks of an electrically insulatingmaterial and a plurality of channels disposed throughout theelectrically insulating material and between the blocks. The flowbattery cell further has an anodic half cell containing an anolyte, ananolyte inlet, an anolyte outlet, an anolyte pathway extending betweenthe anolyte inlet and outlet and within the anodic half cell, and ananode in fluid communication with the anolyte pathway. Also, the flowbattery cell further has an electrolyte membrane disposed between thecathodic half cell and the anodic half cell and in contact with thecatholyte and anolyte, a cathodic contact electrically connected withthe cathode and disposed outside of the cathodic half cell, and ananodic contact electrically connected with the anode and disposedoutside of the anodic half cell.

In many examples, the open block flow screen extends from the catholyteinlet to the catholyte outlet and from the planar cathode to theelectrolyte membrane. The open block flow screen is usually in physicalcontact with the front facing surface of the planar cathode. The blockswithin the open block flow screen may have a variety of shapes,including rectangular geometry, spherical geometry, cylindricalgeometries, as well as irregular three-dimensional geometry. Thechannels of the open block flow screen may occupy about 70% or more ofthe total volume encompassing the open block flow screen. In someembodiments, the open block flow screen may be a porous mat containing afabric or woven material. The fabric or woven material contains channelswhich may have a diameter or a porosity within a range from about 5 μmto about 300 μm, such as from about 10 μm to about 100 μm. In otherembodiments, the open block flow screen contains channels disposedbetween fibers or blocks, such that each fiber or block may have awidth, a length, a height, and/or a diameter each independently within arange from about 10 μm to about 500 μm, such as from about 10 μm toabout 250 μm, or from about 10 μm to about 150 μm, for example, fromabout 10 μm to about 100 μm.

In another embodiment, a flow battery cell is provided which includes acathodic half cell containing a catholyte, a catholyte inlet, acatholyte outlet, a catholyte pathway extending between the catholyteinlet and outlet and within the cathodic half cell, and a slotted sheetcathode in fluid communication with the catholyte pathway and extendingperpendicular or substantially perpendicular to the catholyte pathway.The slotted sheet cathode contains a plurality of cathodic stripsseparated by slots disposed through a metallic sheet (e.g., stainlesssteel).

The slotted sheet cathode may contain iron, steel, stainless steel,cadmium, cadmium plated stainless steel, alloys thereof, or combinationsthereof. In some examples, the slotted sheet cathode may contain or beformed from a stainless steel sheet in which the slots have beenstamped, punched, or otherwise formed there through. Each cathodic stripof the slotted sheet cathode may have a thickness within a range fromabout 0.005 inch to about 0.1 inch, such as, from about 0.01 inch toabout 0.05 inch, for example, about 0.02 inch, and may have a widthwithin a range from about 0.005 inch to about 0.1 inch, such as, fromabout 0.01 inch to about 0.05 inch, for example, about 0.02 inch. Also,each cathodic strip of the slotted sheet cathode may have a lengthwithin a range from about 5 cm (about 1.97 inches) to about 300 cm(about 118.11 inches). In some examples, each cathodic strip may have alength within a range from about 20 cm (about 7.87 inches) to about 200cm (about 78.74 inches), or from about 50 cm (about 19.69 inches) toabout 100 cm (about 39.37 inches). In other examples, each cathodicstrip may have a length within a range from about 5 cm (about 1.97inches) to about 50 cm (about 19.69 inches), such as from about 20 cm(about 7.87 inches) to about 30 cm (about 11.81 inches).

The flow battery cell further includes an anodic half cell containing ananolyte, an anolyte inlet, an anolyte outlet, an anolyte pathwayextending between the anolyte inlet and outlet and within the anodichalf cell, and an anode in fluid communication with the anolyte pathway.The flow battery cell also contains an electrolyte membrane disposedbetween the cathodic half cell and the anodic half cell and in contactwith the catholyte and anolyte. The flow battery cell further contains acathodic contact electrically connected with the slotted sheet cathodeand disposed outside of the cathodic half cell, as well as an anodiccontact electrically connected with the anode and disposed outside ofthe anodic half cell.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the inventioncan be understood in detail, a more particular description of theinvention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIGS. 1A-1C depict a flow battery system containing a flow battery cellhaving an open block flow screen exposed to the catholyte, as describedin one embodiment herein;

FIGS. 2A-2I depict flow battery systems containing variousconfigurations of cathodic wires, as described by embodiments herein;

FIGS. 3A-3F depict a flow battery cell assembly which may beincorporated into a flow battery system, as described by embodimentsherein;

FIG. 4 depicts a flow battery system containing a plurality of varietyof battery cells, as described by embodiments herein;

FIGS. 5A-5C depict a cathodic wire assembly which may be incorporatedinto the flow battery cells, as described by embodiments herein; and

FIGS. 6A-6C depict a flow battery system containing a flow battery cellhaving a slotted sheet cathode, as described in one embodiment herein.

DETAILED DESCRIPTION

Embodiments of the invention generally provide for flow battery cells,flow battery systems containing a plurality of flow battery cells, andmethods for improving metal plating on to a variety of different typesof cathodes within the flow battery cell. The flow battery cellsdescribed herein have improved cathodes and electrolyte flow paths andtherefore provide increased rates for plating metal, uniformity, andmorphology over traditional flow batteries. In embodiments describedherein, the electrode on which metal is plated may be referred to as thecathode and the same half-cell is called the cathodic side during acharging cycle of the battery. However, the current flow in the batteryis reversed and the electrode on which the metal was plated becomes ananode during a discharge cycle of the battery.

In one embodiment, flow battery system 100 contains a flow battery cell102 which has a cathodic half cell 122 and an anodic half cell 142separated by electrolyte membrane 110, as depicted in FIG. 1A. Flowbattery system 100 is illustrated having just one flow battery cell 102,however, flow battery system 100 often contains multiple cells similarto flow battery cell 102. The specific quantity of flow battery cells102 may be determined based on the total capacity of each flow batterycell 102 and the relative total desired energy capacity for the overallflow battery system 100. A plurality of flow battery cells 102 may beconnected together for storing the total desired energy capacity.

Cathodic half cell 122 is on the cathodic side 120 of flow batterysystem 100 and contains a cathode, such as planar cathode 124, which isin fluid communication with catholyte 126. Planar cathode 124 generallyhas a solid surface but may have a variety of geometries, such as a flatplanar cathode or a cylindrical cathode. Planar cathode 124 generalcontains a material such as graphite or a metal, such as nickel, iron,chromium, stainless steel, zinc, cadmium, lead, mercury, alloys thereof,or combinations thereof. In some examples, planar cathode 124 maycontain cadmium-plated iron, or lead-plated iron. In some examples,planar cathode 124 contains graphite. Planar cathode 124 may have acomposite structure and contain a material such as a plastic or polymercontaining graphite fibers, graphite fibers plated with nickel oranother of the aforementioned metals. In other examples, planar cathode124, being a metal or composite structure, may be plated with cadmium.In some embodiments, planar cathode 124 may have a length within a rangefrom about 5 cm to about 300 cm, such as, from about 20 cm to about 200cm, such as, from about 50 cm to about 100 cm. In some examples, planarcathode 124 may have a length within a range from about 10 cm to about50 cm, such as, from about 20 cm to about 30 cm. In some embodiments,planar cathode 124 may have surface area within a range from about 500cm² to about 4,000 cm², such as, from about 1,000 cm² to about 2,000cm².

In another embodiment, the flow battery cell 102 is configured toimprove metal plating uniformity due to the dimensions of the cathodichalf cell 122 which provides an increased velocity for a givenvolumetric fluid velocity of the catholyte 126 along catholyte pathway133. In many configurations, the cathodic half cell 122 may have thelength greater than the height along the catholyte pathway 133 and theheight greater than the width along the catholyte pathway 133. Thisincreased volumetric flow rate in turn provides minimal depletion ofbulk level of chemistry across the length of catholyte pathway 133. Theconcentration of the catholyte 126 stays substantially constant whilemetal is plating on the planar cathode 124. Therefore, flow battery cell102 has a longer length along the flow direction of catholyte pathway133 than a width, which results in the highest fluid velocities for agiven volumetric flow rate. The width of cathodic half cell 122 acrosscatholyte pathway 133 (e.g., between planar cathode 124 and electrolytemembrane 110) may be within a range from about 1 mm to about 20 mm, suchas, from about 5 mm to about 15 mm, for example, about 10 mm. The lengthof cathodic half cell 122 along catholyte pathway 133 (e.g., betweencatholyte inlet 132 and catholyte outlet 134) may be within a range fromabout 5 cm to about 300 cm, such as, from about 20 cm to about 200 cm,such as, from about 50 cm to about 100 cm. The height of cathodic halfcell 122 along catholyte pathway 133 (e.g., normal to the width andlength) may be within a range from about 5 cm to about 300 cm, such as,from about 20 cm to about 200 cm, such as, from about 50 cm to about 100cm. In one example, cathodic half cell 122 may have a length of about200 cm, a height of about 10 cm, and a width of about 10 mm. In anotherexample, cathodic half cell 122 may have a length of about 100 cm, aheight of about 20 cm, and a width of about 10 mm.

Catholyte 126 may be flowed into catholyte inlet 132 which is disposedon cathodic half cell 122, along catholyte pathway 133, and out fromcatholyte outlet 134 disposed on cathodic half cell 122. Catholytepathway 133 extends between catholyte inlet 132 and catholyte outlet 134within cathodic half cell 122. In most embodiments, catholyte 126 is aliquid electrolyte, such as an aqueous based electrolyte. In someexamples, catholyte 126 may be a zinc electrolyte. In one example, thecatholyte for a zinc/ferrocyanide battery is alkaline. The catholyte maycontain a hydroxide concentration within a range from about 1 N to about7 N, such as from about 2 N to about 5 N. The hydroxide may be sodiumhydroxide or potassium hydroxide and may be saturated with zincate. Insome examples, the catholyte 126 may be saturated or supersaturated,such that zincate precipitates in the bath forming solid suspensions.

Outside of flow battery cell 102, catholyte 126 circulates betweencathodic half cell 122 and catholyte source tank 130 by conduits 136.Conduits 136 extend between catholyte source tank 130 to catholyte inlet132 and from catholyte outlet 134 to catholyte source tank 130. One ormultiple pumps, such as pump 138, may be incorporated within flowbattery system 100 to help flow catholyte 126 to and from cathodic halfcell 122. In some examples, pump 138 may be disposed between catholytesource tank 130 and catholyte inlet 132 and connected therebetween byconduits 136. In other examples, pump 138 may be disposed betweencatholyte source tank 130 and catholyte outlet 134 and connectedtherebetween by conduits 136. Therefore, in one specific example,catholyte 126 may circulate within the cathodic side 120 of flow batterysystem 100 by flowing from catholyte source tank 130, through conduits136, through catholyte inlet 132, along catholyte pathway 133 and withinchannels 164 of open block flow screen 160 within cathodic half cell122, through catholyte outlet 134, through conduits 136, and back tocatholyte source tank 130.

In one embodiment, an open block flow screen 160 is disposed withincatholyte pathway 133, as depicted in FIGS. 1A-1C. Open block flowscreen 160 contains a plurality of blocks 162 of an electricallyinsulating material and a plurality of channels 164 disposed throughoutthe electrically insulating material and between blocks 162. Open blockflow screen 160 helps to provide uniform ion transfer throughout andalong the long thin channels 164 within catholyte 126.

In some embodiments, open block flow screen 160 extends from catholyteinlet 132 to catholyte outlet 134 and/or from planar cathode 124 toelectrolyte membrane 110. In some examples, open block flow screen 160may be in physical contact with the front facing surface of planarcathode 124. The channels 164 of open block flow screen 160 may occupyabout 50% or more of the total volume encompassing open block flowscreen 160, such as about 70% or more, or about 75% or more. Therefore,open block flow screen 160 has an open structure since the volume ofchannels 164 occupies more volume than the volume of blocks 162.

The width of open block flow screen 160 may be the same, substantiallythe same, or less than the total gap distance between planar cathode 124and electrolyte membrane 110, such as the width of cathodic half cell122. The width of open block flow screen 160 may be within a range fromabout 1 mm to about 20 mm, such as, from about 1 mm to about 10 mm, forexample, about 1.5 mm, about 3.5 mm, or about 10 mm. The length of openblock flow screen 160 may be the same, substantially the same, or lessthan the distance between catholyte inlet 132 and catholyte outlet 134,such as the length of cathodic half cell 122 or the length of catholytepathway 133. The length of open block flow screen 160 may be within arange from about 5 cm to about 300 cm, such as, from about 5 cm to about200 cm, such as, from about 5 cm to about 100 cm, for example, fromabout 5 cm to about 50 cm, such as, from about 10 cm to about 30 cm,such as about 12 cm or about 20 cm.

The plurality of blocks 162 of open block flow screen 160 may have avariety of different geometries, but preferably have a three-dimensionpolygonal geometry, such rectangular prism geometries (e.g., cubicalgeometry), spherical geometries, cylindrical geometries, as well asirregular three-dimensional geometries. In some embodiments, open blockflow screen 160 may be a porous mat containing a fabric or wovenmaterial, such as fibers. A plurality of channels extends between thefibers and throughout the fabric or woven material of open block flowscreen 160. The fibers may have a diameter or a thickness within a rangefrom about 10 μm to about 300 μm, such as from about 10 μm to about 200μm. The plurality of channels have a diameter or a porosity within arange from about 5 μm to about 300 μm, from about 10 μm to about 250 μm,such as from about 10 μm to about 150 μm or from about 10 μm to about100 μm. In one example, open block flow screen 160 contains channelswhich have a diameter or a porosity within a range from about 10 μm toabout 100 μm.

In other embodiments, each block 162 of open block flow screen 160 mayhave a width within a range from about 10 μm to about 500 μm, such asfrom about 10 μm to about 250 μm, or from about 10 μm to about 150 μm,for example, from about 10 μm to about 100 μm, a length within a rangefrom about 10 μm to about 500 μm, such as from about 10 μm to about 250μm, or from about 10 μm to about 150 μm, for example, from about 10 μmto about 100 μm, and a height within a range from about 10 μm to about500 μm, such as from about 10 μm to about 250 μm, or from about 10 μm toabout 150 μm, for example, from about 10 μm to about 100 μm. The channelpassing through the blocks may have a diameter or a porosity within arange from about 5 μm to about 300 μm, from about 10 μm to about 250 μm,such as from about 10 μm to about 150 μm or from about 10 μm to about100 μm. In some examples, each block 162 may be cubical and have a widthof about 125 μm, a length of about 125 μm, and a height of about 125 μm.In other examples, each block 162 may be cubical and have a width ofabout 625 μm, a length of about 625 μm, and a height of about 625 μm.

In embodiments described herein, open block flow screen 160 may containor be composed of an electrically insulating material, such as apolymeric material, a co-polymeric material, or an oligomeric material.Open block flow screen 160 may contain or be made from exemplarymaterials such as polyethylene, polypropylene, natural polypropylene(NPP), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyvinylchloride (PVC), polyvinylidene fluoride (PVDF), fluorinated ethylenepropylene (FEP), perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE),as well as other fluoropolymers, derivatives thereof, or combinationsthereof. In one example, open block flow screen 160 containspolypropylene or derivatives thereof. In some embodiments, open blockflow screen 160 may contain a woven plastic material which is inert tothe electrolyte, such as a woven fabric of fibers containingpolypropylene or derivatives thereof. Open block flow screen 160 may besparse in the direction parallel with the electrolyte flow.

Anodic half cell 142 is on the anodic side 140 of flow battery system100 and contains an anode, such as anode 144, which may be in fluidand/or conductive communication with anolyte 146. Anolyte 146 may be aliquid electrolyte, such as an aqueous based electrolyte or a solidelectrolyte. In embodiments when anolyte 146 is a liquid anolyte,anolyte 146 flows into anolyte inlet 152 disposed on anodic half cell142, along anolyte pathway 153, and out from anolyte outlet 144 disposedon anodic half cell 142. Anolyte pathway 153 extends between anolyteinlet 152 and anolyte outlet 154, as well as between anode 144 andelectrolyte membrane 110 within anodic half cell 142.

Outside of flow battery cell 102, in embodiments when anolyte 146 is aliquid anolyte, anolyte 146 circulates between anodic half cell 142 andanolyte source tank 150 by conduits 156. Conduits 156 extend betweenanolyte source tank 150 to anolyte inlet 152 and from anolyte outlet 154to anolyte source tank 150. One or multiple pumps, such as pump 158, maybe incorporated within flow battery system 100 to help flow anolyte 146to and from anodic half cell 142. In some examples, pump 158 may bedisposed between anolyte source tank 150 and anolyte inlet 142 andconnected therebetween by conduits 156. In other examples, pump 158 maybe disposed between anolyte source tank 150 and anolyte outlet 134 andconnected therebetween by conduits 156. Therefore, in one specificexample, anolyte 146 may circulate within the anodic side 140 of flowbattery system 100 by flowing from anolyte source tank 150, throughconduits 156, through anolyte inlet 152, along anolyte pathway 153within anodic half cell 142, through anolyte outlet 154, throughconduits 156, and back to anolyte source tank 150.

In some embodiments, anolyte 146 may be a solid anolyte, and therefore,certain portions or elements of the anodic side 140, as depicted in FIG.1A, may be optional or absent portions or derivatives thereof, such asanolyte inlet 152, anolyte outlet 154, anolyte source tank 150, conduits156, and/or pump 158. A solid anolyte 246 may have a thickness within arange from about 0.2 mm to about 5 mm, or from about 0.5 mm to about 3mm, such as about 1 mm or about 2 mm.

In some examples, anolyte 146 may be an Fe(II)/Fe(III) electrolyte, suchas a ferro/ferricyanide electrolyte. Anolyte 146 may initially contain aferrocyanide compound which is oxidized to the respective ferricyanidecompound during a recharge of the battery or cell. Several exemplaryferrocyanide compounds that may be contained within the anolyte 146include sodium ferrocyanide, such as tetrasodium hexacyanoferratedecahydrate (Na₄Fe(CN)₆.10H₂O), also known as yellow prussiate of soda,available from ScienceLab.com, as well as potassium ferrocyanide, suchas tetrapotassium hexacyanoferrate decahydrate (K₄Fe(CN)₆.10H₂O).Anolyte 146 generally contains hydroxide and additional hydroxidesolution may be added to the anolyte 146 during the charge/dischargecycles in order to maintain a desired hydroxide concentration. Theaqueous hydroxide solution generally contains sodium hydroxide,potassium hydroxide, or mixtures thereof.

Anode 144, such as a redox electrode, may have a variety of geometries,such as a flat planar anode, a planar anode, a plate anode, acylindrical anode, or the like. Anode 144 may be may be solid, or mayhave a high surface area configuration, such as being porous, expandedor foamed. Usually, anode 144 contains nickel, iron, chromium, steel,stainless steel, graphite, alloys thereof, derivatives thereof, orcombinations thereof. Anode 144 may be plated or coated with anothermaterial or metal, such as a graphite anode coated or plated with nickelor a nickel alloy. In one example, anode 144 is a planar electrode andcontains stainless steel. In another example, anode 144 is porous,foamed, or expanded and contains nickel or a nickel alloy, such asnickel foam, expanded nickel, perforated nickel, nickel wire, or wovennickel wire. In another example, anode 144 contains graphite, such asporous graphite, graphite foam, nickel plated graphite foam, graphitefelt, nickel plated graphite felt, or derivatives thereof. In someembodiments, anode 144 may have a length within a range from about 5 cmto about 300 cm, such as from about 10 cm to about 50 cm, such as fromabout 20 cm to about 30 cm and may have a height within a range fromabout 5 cm to about 300 cm, such as from about 10 cm to about 50 cm,such as from about 20 cm to about 30 cm. Additionally, anode 144 mayhave a thickness within a range from about 0.5 mm to about 5 mm, such asfrom about 1 mm to about 3 mm.

Electrolyte membrane 110 is disposed between cathodic half cell 122 andanodic half cell 142 and in contact with both catholyte 126 and anolyte146. Electrolyte membrane 110 may be an exchange membrane, a separator,or the like which isolates catholyte 126 and anolyte 146. In manyembodiments, electrolyte membrane 110 is an ionic exchange membrane—suchas a cationic exchange membrane—which is semipermeable to some cations(e.g., Na+ or K+) which migrate through electrolyte membrane 110 betweenthe anolyte 146 and catholyte 126. Electrolyte membrane 110 may containor be made from an ionic resin and/or a polymeric, co-polymeric, oroligomeric material, such as polytetrafluoroethylene, polyvinyl,polystyrene, polyethylene, polypropylene, polyester, derivativesthereof, or combinations thereof. Generally, electrolyte membrane 110 isdurable and has high ionic conductivity and chemical stability. In oneexample, electrolyte membrane 110 contains a polymeric backbone ofpolytetrafluoroethylene (PTFE), such as NAFION® 112, 115, 117, and 424membranes, which are commercially available from DuPont. In anotherexample, electrolyte membrane 110 contains a co-polymer oftetrafluoroethylene and a vinylene monomer, such as a XUS® membrane,which is commercially available from Dow Chemical Company. Electrolytemembrane 110 may have a thickness within a range from about 0.005 mm toabout 0.5 mm. In some examples, electrolyte membrane 110 may have athickness of about 0.015 mm. In an alternative embodiment, electrolytemembrane 110 may be a separator, such as a ribbed separator, formed froma polymeric material and precipitated silica, such that the internalstructure is very porous, tortuous, and hydrophilic (e.g., hydrophilicporous plastic separator), which is commercially available from theAMER-SIL company.

Cathodic contact 172 is in electrical contact to planar cathode 124 andanodic contact 174 is in electrical contact to anode 144, as depicted inFIG. 1A. Cathodic contact 172 may be disposed on flow battery cell 102and extends between the inside and outside of cathodic half cell 122.Similarly, anodic contact 174 may be disposed on flow battery cell 102and extends between the inside and outside of anodic half cell 142.

Cathodic contact 172 and anodic contact 174 may be coupled to orotherwise in electrical contact with for discharging or removing thestored power from flow battery cell 102 while in use, or alternatively,for charging or storing power to flow battery system 100. Each flowbattery cell 102 may be electrically connected (e.g., in parallel or inseries) with cathodic contacts 172 and anodic contacts 174 to form thedesirable circuit for flow battery system 100. In one example, theplurality of flow battery cells 102 may be electrically connected inseries in order to have constant amperage and increased voltage for flowbattery system 100. Alternatively, the plurality of flow battery cells102 may be electrically connected in parallel in order to have constantvoltage and increased amperage for flow battery system 100.

Open block flow screen 160 causes flow disruption of catholyte 126thereby periodically disturbs the diffusion layer on planar cathode 124while plating a metal which keeps the plating of metal much more uniformacross planar cathode 124 compared to processes in which metal wasplated to a traditional planar electrode in the absence of open blockflow screen 160. Instead of a continuous drop in the plating rate acrossplanar cathode 124, the current density has much smaller non-uniformity(e.g., about 15% to about 30%) that repeats according to the scale ofblocks 162 and channels 164 of open block flow screen 160. The smallerand non-uniform current density is due to better mixing of catholyte 126and therefore allows charging/discharging at a higher current densityrelative to planar cathode 124 without the open block flow screen 160.

Catholyte 126 may have a forward flow (as depicted in FIG. 1A witharrows) or may have a reverse flow during different time periods of thecharge/discharge cycles. The fluid velocity of catholyte 126 may bewithin a range from about 1 cm/sec (centimeter/second) to about 25cm/sec, such as from about 2 cm/sec to about 15 cm/sec, for example,about 5 cm/sec or about 10 cm/sec. Anolyte 146 may have a forward flow(as depicted in FIG. 1A with arrows) or may have a reverse flow duringdifferent time periods of the charge/discharge cycles. The fluidvelocity of anolyte 146 may be within a range from about 1 cm/sec toabout 25 cm/sec, such as from about 2 cm/sec to about 15 cm/sec, forexample, about 5 cm/sec or about 10 cm/sec. The planar cathode 124combined with open block flow screen 160 may have a localized currentdensity within a range from about 1 mA/cm² (milliamps per squaredcentimeters) to about 75 mA/cm², such as from about 5 mA/cm² to about 50mA/cm², for example, about 10 mA/cm², about 20 mA/cm², or 40 mA/cm².

FIGS. 2A-2I depict a flow battery system 200 containing a flow batterycell 202 which has a cathodic half cell 222 and an anodic half cell 242separated by electrolyte membrane 210, as described in multipleembodiments herein. Cathodic half cell 222 is on the cathodic side 220of flow battery system 200 and has a cathode containing a plurality ofcathodic wires 228, which extend through and are in fluid communicationwith catholyte 226 in catholyte pathway 233. The pluralities of cathodicwires 228 extend perpendicular or substantially perpendicular tocatholyte pathway 233 and each of the cathodic wires 228 extendsparallel or substantially parallel to each other.

The flow battery system 200 depicted in FIGS. 2A-2I and described byembodiments herein provide a plurality of cathodic wires 228 whichgenerally produce more uniform metal plating when compared totraditional planar electrodes. Cathodic wires 228 placed perpendicularor substantially perpendicular to the flow path of the electrolyte(e.g., catholyte 226) which provide many performance improvements forthe flow battery cells 202. Flow battery system 200 generally has ahigher cell current density while keeping the current density on thewires reasonable (e.g., a low fraction of the limiting current)—which inturn leads to a higher battery charge rate relative to a traditionalbattery. Flow battery system 200 containing cathodic wires 228 generallyhas a larger metal storage capacity leading to larger discharge times ata given current density, relative to traditional flow batteries. Thesequential plating of various arrays of electrodes—such as cathodicwires 228—helps to achieve longer discharge times for flow batterysystem 200, as well as to provide in-situ electrode maintenance to avoiddowntime for electrode reconditioning—as compared to a traditionalplanar electrode. For example, when deplating metal off one array ofcathodic wires 228 during a battery discharge, another array of cathodicwires 228 may have a small trickle discharge to insure complete orsubstantially complete removal of the plated metal. The cathodic wires228 generally provide plating and deplating rates which are more uniformand yield good performance over many charge/discharge cycles—as comparedto a traditional planar electrode. The cathodic wires 228 yield a largesurface area with a relative low volume of metal contained therein. Thelarge surface area of the cathodic wires 228 generally provides lowercell voltage drop and higher cell efficiency—as compared to atraditional planar electrode. In some examples, the surfaces of thecathodic wires 228 contain cadmium, such as a solid cadmium wire, acadmium coated steel wire, or the like and the catholyte 226 containsmetal ions (e.g., zinc ions) which are electrochemically reduced andplated onto the cathodic wires 228 as a metal film (e.g., metallic zinc)during a charge cycle of flow battery cell 202 or flow battery system200.

In one embodiment, FIGS. 2A-2B depict cathodic half cell 222 containinga single row of cathodic wires 228 within catholyte pathway 233. Thesingle row of cathodic wires 228 extend along catholyte pathway 233while each individual cathodic wire 228 extends perpendicular orsubstantially perpendicular to catholyte pathway 233. Catholyte 226 isflowed through cathodic half cell 222 and along catholyte pathway 233while being exposed to the cathodic wires 228. The cathodic wires 228electrochemically reduce the metal ions from the catholyte while platingthe surfaces of the cathodic wires 228 during the charging cycles andelectrochemically oxidize the plated metal from the surfaces of thecathodic wires 228 to form metal ions which diffuse back into thecatholyte 226 during the discharging cycles. Catholyte pathway 233extends between catholyte inlet 232 and catholyte outlet 234 which aredisposed on opposite sides if the cathodic half cell 222.

Each of the cathodic wires 228 may independently have various geometriesor shapes such as cylindrical, rectangular, oval, derivatives thereof,as well as other geometries. The cathodic wires 228 may be cylindricalwires or wires having at least one side, such as a rectangular wire or asquare wire. The cathodic wires 228 may be solid wires, hollow wires ortubes, ribbons, rods, bars, strips, or derivatives thereof. Each of thecathodic wires, including cathodic wires 228, 228 a, or 228 b, mayindependently contain a metal, such as cadmium, iron, steel, stainlesssteel, nickel, chromium, silver, gold, platinum, palladium, platings orcoatings thereof, alloys thereof, derivatives thereof, or combinationsthereof. In some examples, each of the cathodic wires contains cadmiumor a cadmium alloy. Each cathodic wire may be a solid cadmium wire, asolid cadmium alloy wire, a cadmium plated metallic wire, such as asteel or stainless steel wire plated or coated with cadmium or a cadmiumalloy. In one example, the cathodic wires are solid wires containingcadmium or a cadmium alloy.

The cathodic wires 228 are generally spaced a predetermined distancefrom each other within the row of cathodic wires 228. In someembodiments, the predetermined distance may be equal to or substantiallyequal to the circumference of the individual cathodic wire 228. Thepredetermined distance or spacing between the cathodic wires 228provides sufficient space for plates to grow around each cathodic wire228, and leave room to sustain good mass-transfer and avoid the metalaccumulation from causing the wires to touch. The predetermined distanceor spacing between the cathodic wires 228 provides enough time for awake formed behind one cathodic wire 228 to sufficiently “heal” so thatthe next downstream cathodic wire 228 still receives adequatemass-transfer from the catholyte 226. The wake is a portion or volume ofthe catholyte 226 having a reduced gradient concentration of one or morecomponents such as the metal ions within the catholyte 226. However, asthe wake flows downstream, the remaining metal ions within the catholyte226 diffuse throughout the catholyte 226 to reduce or remove the wakewhile exposing the next downstream cathodic wire 228. Therefore, thepredetermined distance or spacing between the cathodic wires 228provides enough time for abundant or higher concentrations of componentsin one region to diffuse through the catholyte 226 to regions havingshortages or lower concentrations of that component.

In another embodiment described herein, the total surface area of allcathodic wires 228 within the row may be equal to or substantially equalto the surface area of a more traditional planar electrode found inother flow batteries. Therefore, the surface area available for metalplating during the charging cycles may be adjusted by adding or removingindividual cathodic wires 228 to or from cathodic half cell 222.Similarly, if the surface area of a single row of cathodic wires 228 hasbeen normalized and equivalent to the surface area of a traditionalplanar electrode, than each additional row of cathodic wires 228 may beincluded within cathodic half cell 222 to provide the platingequivalents to the same number of traditional planar electrodes. Theaddition of cathodic wires 228 within cathodic half cell 222 providesadditional surface area for having better control of the quality of thedeposited metal film, as well as, more metal storage or energy storage.

FIG. 2B depicts contact bar 229 coupled to and in electrical contactwith each of the cathodic wires 228. One contact bar 229 is depicted inFIG. 2B, however, numerous contact bars may be used to individuallycontrol each cathodic wire 228 or an array of cathodic wires 228.Contact bar 229 may be disposed inside or outside the cathodic half cell222, or within any of the surrounding walls or surfaces of cathodic halfcell 222, such as the bottom portion 212, the top portion 214, and/orthe sides 216 of cathodic half cell 222. In some embodiments, contactbar 229 may be disposed within the top portion 214 of cathodic half cell222, as depicted in FIG. 2B. In other embodiments, contact bar 229 maybe disposed outside of the surrounding walls or surfaces of cathodichalf cell 222. For example, contact bar 229 or a contact junctionthereof may protrude through the bottom portion 212, the top portion214, and/or the sides 216 of cathodic half cell 222 to be physically andelectrically coupled with each of the cathodic wires 228, as depicted inFIG. 2D or 2F. Alternatively, each of the cathodic wires 228 mayprotrude through the bottom portion 212, the top portion 214, and/or thesides 216 of cathodic half cell 222 to be physically and electricallycoupled with contact bar 229. Contact bar 229 contains a conductivematerial, such as a metal. Contact bar 229 may be a wire, a plate, abar, a ribbon, or similar contact/conductive surface. Contact bar 229may contain iron, steel, stainless steel, copper, nickel, chromium,silver, gold, aluminum, cadmium, platinum, palladium, platings thereof,alloys thereof, derivatives thereof, or combinations thereof. In someembodiments, contact bar 229 may also in electrical contact withcathodic contact 262.

In one embodiment, contact bar 229 may be the same wire used as thecathodic wires 228. A wire may be incorporated into cathodic half cell222 by weaving the wire between the catholyte pathway 233 and throughthe bottom and top portions 212 and 214 of cathodic half cell 222. Insome examples, the wire may be a solid cadmium wire, a solid cadmiumalloy wire, a cadmium plated metallic wire, such as a steel or stainlesssteel wire plated with cadmium or a cadmium alloy.

FIGS. 2C-2F depict cathodic half cell 222 containing two rows ofcathodic wires 228 a and 228 b, as described by other embodimentsherein. FIGS. 2C-2D depict two staggered rows of cathodic wires 228 aand 228 b exposed to catholyte within catholyte pathway 233. Both rowsof cathodic wires 228 a and 228 b extend along catholyte pathway 233while each individual cathodic wire 228 extends perpendicular orsubstantially perpendicular to catholyte pathway 233. Each cathodic wire228 a within the row closest to the electrolyte membrane 210 is coupledwith contact bar 229 a while each cathodic wire 228 b in the rowfurthest from the electrolyte membrane 210 is coupled with contact bar229 b, as depicted in FIG. 2D. Therefore, each row of the cathodic wires228 a and 228 b may be independently connected or disconnectedelectrically from the cathodic contact 262 via contact bars 229 a and229 b. Cathodic wires 228 a and 228 b which are electrically connectedto cathodic contact 262 are referred to as “energized” cathodic wireswhile cathodic wires 228 a and 228 b which are electrically disconnectedto cathodic contact 262 are referred to as “non-energized” cathodicwires. Also, each row of the cathodic wires 228 a and 228 b may besimultaneously or sequentially connected or disconnected electricallyfrom the cathodic contact 262.

A controller and/or a set of switches (not shown) may be coupled betweenand in electrical communication to the cathodic contact 262 and each ofthe contact bars 229 a and 229 b. The controller and/or the set ofswitches may be used to independently control by electricallyconnecting/disconnecting each of the contact bars 229 a and 229 b—andtherefore each row of the cathodic wires 228 a and 228 b—to the cathodiccontact 262. In some configurations, the controller and/or the set ofswitches may be used to independently charge and/or discharge each rowof the cathodic wires 228 a and 228 b. Once in electrical contact withcathodic contact 262, the cathodic wires 228 a and 228 b within bothrows are energized cathodic wires which are capable of beingplated/deplated during charge/discharge cycles.

For example, as depicted by FIGS. 2E-2F, metal from a first array ofelectrodes, cathodic wires 228 b, is deplating during the discharge ofthe flow battery cell 202, while a second array of electrodes, cathodicwires 228 a, is electrically disconnected from the cathodic contact 262.Initially, cathodic wires 228 b are energized cathodic wires which areelectrically connected to the cathodic contact 262 while cathodic wires228 a are non-energized cathodic wires. The power produced by the flowbattery cell 202 is eventually reduced to an inefficient trickle chargesuch that the produced power is below a predetermined minimum thresholdfor desirable battery performance. This reduction of power isproportional to the reduction of the total surface area of the cathodicwires 228 b—which are both caused by the deplating of metal from thecathodic wires 228 b. Therefore, the second array electrodes, cathodicwires 228 a, containing a full metal plating, is energized orelectrically connected to the cathodic contact 262 by the contact bar229 a. The first array of electrodes, cathodic wires 228 b, may be leftenergized or electrically connected to the cathodic contact 262 by thecontact bar 229 b until substantially or completely deplated of metal.Alternatively, the cathodic wires 228 b may be non-energized orelectrically disconnected from the cathodic contact 262.

Although FIGS. 2E-2F depict the cathodic wires 228 a as being initiallyenergized cathodic wires and the cathodic wires 228 b as being initiallynon-energized cathodic wires, in other embodiments, a charge/dischargecycle of the flow battery cell 202 or the flow battery system 200 may beperformed in the reverse order. Therefore, the first array of electrodesmay be the cathodic wires 228 a which initially are energized anddeplate metal during the discharge of the flow battery cell 202, whilethe cathodic wires 228 b—the second array of electrodes—remainnon-energized or electrically disconnected from the cathodic contact262. Once the flow battery cell 202 is producing power below thepredetermined minimum threshold, the cathodic wires 228 b are energizedor placed in electrical contact to the cathodic contact 262 by thecontact bar 229 b. The cathodic wires 228 a may be left energized suchas to remain in electrical contact to the cathodic contact 262 by thecontact bar 229 a in order to deplate remaining metal thereon. In analternative embodiment, both rows of the cathodic wires 228 a and 228 bmay be simultaneously energized cathodic wires during thecharge/discharge cycles of the flow battery cell 202 or the flow batterysystem 200.

In another embodiment, FIGS. 2G-2I depict cathodic half cell 222containing four rows of cathodic wires 228, such as two rows of cathodicwires 228 a and two rows of cathodic wires 228 b, as described by otherembodiments herein. FIG. 2G depicts four staggered rows of cathodicwires 228 exposed to catholyte within catholyte pathway 233. The fourrows of cathodic wires 228 extend along catholyte pathway 233 while eachindividual cathodic wire 228 extends perpendicular or substantiallyperpendicular to catholyte pathway 233. Each of the four rows ofcathodic wires 228 is independently coupled with and in electricalcontact to an independent contact bar (not shown) similar to contactbars 229 a or 229 b.

Therefore, each row of the cathodic wires 228 may be independentlyconnected (energized) or disconnected (non-energized) electrically fromthe cathodic contact 262 via contact bars. A controller and/or a set ofswitches (not shown) are coupled between and in electrical communicationto the cathodic contact 262 and each of the contact bars. The controllerand/or the set of switches may be used to independently control byelectrically connecting/disconnecting each of the contact bars—andtherefore each row of the cathodic wires 228—to the cathodic contact262. In some configurations, the controller and/or the set of switchesmay be used to independently control charge and/or discharge each row ofthe cathodic wires 228. Once in electrical contact with cathodic contact262, the cathodic wires 228 within all four rows are capable of beingplated/deplated during charge/discharge cycles.

FIGS. 2H-2I illustrate a first array of electrodes containing twostaggered rows of cathodic wires 228 a which are closest to theelectrolyte membrane 210, and a second array of electrodes containingtwo staggered rows of cathodic wires 228 b which are furthest from theelectrolyte membrane 210. FIG. 2H depicts both rows of cathodic wires228 b in the first array as deplating during the discharge of the flowbattery cell 202, while both rows of cathodic wires 228 a in the secondarray remain electrically disconnected from the cathodic contact 262.Alternatively, FIG. 2I depicts both rows of cathodic wires 228 a in thefirst array as deplating during the discharge of the flow battery cell202, while both rows of cathodic wires 228 b in the second array remainelectrically disconnected from the cathodic contact 262. In eitherscenario, once the flow battery cell 202 is producing power below thepredetermined minimum threshold, both rows of chargedelectrodes—cathodic wires 228 b (FIG. 2H) or cathodic wires 228 a (FIG.2I) are placed in electrical contact to the cathodic contact 262 bycontact bars, as described above.

In many of the embodiments described herein, the flow battery cell 202operates at a high overall current density by simultaneously energizingmultiple rows of cathodic wires 228 thereby lowering the localizedplating current density of the plated metal on each cathodic wire 228.The overall current density of the flow battery cell 202 is the totalcurrent density across the membrane. The localized plating currentdensity of the cathodic wires 228 is the current density of a single rowof cathodic wires 228. The localized plating current density of aplurality of cathodic wires 228 varies to the quantity of the cathodicwires 228 as well as the diameter of the cathodic wires 228. In oneembodiment, cathodic half cell 222 has a single row of cathodic wires228 (FIGS. 2A-2B) which may produce an overall current density—which isequivalent to the localized plating current density of the one row ofcathodic wires 228—within a range from about 1 mA/cm² to about 40mA/cm², such as from about 5 mA/cm² to about 30 mA/cm², for example,about 20 mA/cm². In another example, cathodic half cell 222 has two rowsof cathodic wires 228 (FIGS. 2C-2F) which may produce an overall currentdensity within a range from about 5 mA/cm² to about 60 mA/cm², such asfrom about 10 mA/cm² to about 50 mA/cm², for example, about 40 mA/cm².In another example, cathodic half cell 222 has four rows of cathodicwires 228 (FIGS. 2G-2I) which may produce an overall current densitywithin a range from about 10 mA/cm² to about 120 mA/cm², such as fromabout 20 mA/cm² to about 100 mA/cm², for example, about 80 mA/cm².

In embodiments described herein, flow battery systems 200 and flowbattery cells 202 utilize at least one row and usually multiple rows ofcathodic wires 228 within the cathodic half cell 222. A reduction ofcost and size are among many advantages provided by cathodic wires 228.From a cost perspective, it is generally beneficial to keep the surfacearea of certain components within a flow battery as small as possible,especially for the higher cost components. Some of these high costcomponents include redox electrodes (e.g., nickel foam) which may beutilized as the anode 244 as well as membranes which may be useful asthe electrolyte membrane 210. The flow multiple rows of cathodic wires228, where each row of cathodic wires 228 contains a small volume ofmetal relative to the provided localized plating current density.

For example, a traditional planar cathode within a flow battery may havea localized plating current density of about 40 mA/cm² on the cathode ifthe plating rate is set to about 40 mA/cm²—therefore—the overall currentdensity through the membrane is also about 40 mA/cm². However, in oneexample described herein, a flow battery system 200 may have two rows ofcathodic wires 228, such that each row of cathodic wires 228 has thesame surface area as the traditional planar electrode. The two rows ofcathodic wires 228 with twice the surface area may be platedsimultaneously at the same rate of about 40 mA/cm² to produce an overallcurrent density (e.g., across electrolyte membrane 210) of about 80mA/cm². Therefore, in this example, a flow battery system 200 maycontain half as many flow battery cells 202 to produce the same power asfrom a conventional flow battery containing traditional planar cathodes.The conventional flow battery may require two battery cells with batterycell containing a traditional planar cathode in order to provide about80 mA/cm². However, in this example, a flow battery system 200 maycontain only one flow battery cell 202 while providing an overallcurrent density of about 80 mA/cm². Therefore, flow battery system 200may provide equivalent power—as the conventional flow battery containingtraditional planar cathodes—while only using half the electrolytemembrane and redox electrode surface areas as well as other expensivecomponents.

In many embodiments, each of the cathodic wires 228 may have the same orsubstantially the same length as the height of the flow battery cell202. Each of the cathodic wires 228 may independently have a lengthwithin a range from about 5 cm to about 300 cm. In some examples, eachof the cathodic wires 228 may independently have a length within a rangefrom about 10 cm to about 50 cm, such as from about 20 cm to about 30cm. In other examples, each of the cathodic wires 228 may independentlyhave a length within a range from about 20 cm to about 200 cm, or fromabout 50 cm to about 100 cm. The cathodic wires may have a diameterwithin a range from about 0.001 inch to about 0.1 inch, such as, fromabout 0.005 inch to about 0.05 inch, or such as, from about 0.01 inch toabout 0.04 inch, or such as, from about 0.02 inch to about 0.03 inch,for example, about 0.012 inch, 0.024 inch or 0.036 inch.

In another embodiment, the flow battery cell 202 is configured toimprove metal plating uniformity due to the dimensions of the cathodichalf cell 222 which provides an increased velocity for a givenvolumetric fluid velocity of the catholyte 226 along catholyte pathway233. In many configurations, the cathodic half cell 222 may have thelength greater than the height along the catholyte pathway 233 and theheight greater than the width along the catholyte pathway 233. Thisincreased volumetric flow rate in turn provides minimal depletion ofbulk level of chemistry across the length of catholyte pathway 233. Theconcentration of catholyte 226 stays substantially constant while metalis plating on the cathodic wires 228. Therefore, flow battery cell 202has a longer length along the flow direction of catholyte pathway 233than a width, which results in the highest fluid velocities for a givenvolumetric flow rate. The width of cathodic half cell 222 acrosscatholyte pathway 233 (e.g., normal the length and height) may be withina range from about 1 mm to about 20 mm, such as, from about 5 mm toabout 15 mm, for example, about 10 mm. The length of cathodic half cell222 along catholyte pathway 233 (e.g., between catholyte inlet 232 andcatholyte outlet 234) may be within a range from about 5 cm to about 300cm, such as, from about 20 cm to about 200 cm, such as, from about 50 cmto about 100 cm. The height of cathodic half cell 222 along catholytepathway 233 (e.g., between bottom and top portions 212 and 214) may bewithin a range from about 5 cm to about 300 cm, such as, from about 20cm to about 200 cm, such as, from about 50 cm to about 100 cm. In oneexample, cathodic half cell 222 may have a length of about 200 cm, aheight of about 10 cm, and a width of about 10 mm. In another example,cathodic half cell 222 may have a length of about 100 cm, a height ofabout 20 cm, and a width of about 10 mm.

In most embodiments, catholyte 226 is a liquid electrolyte, such as anaqueous based electrolyte. In some examples, catholyte 226 may be a zincelectrolyte. In one example, the catholyte for a zinc/ferrocyanidebattery is alkaline. The catholyte may contain a hydroxide concentrationwithin a range from about 1 N to about 7 N, such as from about 2 N toabout 5 N. The hydroxide may be sodium hydroxide or potassium hydroxideand may be saturated with zincate. In some examples, the catholyte 226may be saturated or supersaturated, such that zincate precipitates inthe bath forming solid suspensions.

Outside of flow battery cell 202, catholyte 226 circulates betweencathodic half cell 222 and catholyte source tank 230 by conduits 236.Conduits 236 extend between catholyte source tank 230 to catholyte inlet232 and from catholyte outlet 234 to catholyte source tank 230. One ormultiple pumps, such as pump 238, may be incorporated within flowbattery system 200 to help flow catholyte 226 to and from cathodic halfcell 222. In some examples, pump 238 may be disposed between catholytesource tank 230 and catholyte inlet 232 and connected therebetween byconduits 236. In other examples, pump 238 may be disposed betweencatholyte source tank 230 and catholyte outlet 234 and connectedtherebetween by conduits 236. Therefore, in one specific example,catholyte 226 may circulate within the cathodic side 220 of flow batterysystem 200 by flowing from catholyte source tank 230, through conduits236, through catholyte inlet 232, along catholyte pathway 233 and aroundthe cathodic wires 228 within cathodic half cell 222, through catholyteoutlet 234, through conduits 236, and back to catholyte source tank 230.Catholyte 226 may have a forward flow (as depicted in FIGS. 2A, 2C, 2E,and 2G-2I with arrows) or may have a reverse flow during different timeperiods of the charge/discharge cycles. The fluid velocity of catholyte226 may be within a range from about 1 cm/sec to about 25 cm/sec, suchas from about 2 cm/sec to about 15 cm/sec, for example, about 5 cm/secor about 10 cm/sec.

Anodic half cell 242 is on the anodic side 240 of flow battery system200 and contains anode 244, which may be in fluid and/or conductivecommunication with anolyte 246. Anolyte 246 may be a liquid electrolyte,such as an aqueous based electrolyte or a solid electrolyte. Inembodiments when anolyte 246 is a liquid anolyte, anolyte 246 flows intoanolyte inlet 252 disposed on anodic half cell 242, along anolytepathway 253, and out from anolyte outlet 244 disposed on anodic halfcell 242. Anolyte pathway 253 extends between anolyte inlet 252 andanolyte outlet 254, as well as between anode 244 and electrolytemembrane 210 within anodic half cell 242.

Outside of flow battery cell 202, in embodiments when anolyte 246 is aliquid anolyte, anolyte 246 circulates between anodic half cell 242 andanolyte source tank 250 by conduits 256. Conduits 256 extend betweenanolyte source tank 250 to anolyte inlet 252 and from anolyte outlet 254to anolyte source tank 250. One or multiple pumps, such as pump 258, maybe incorporated within flow battery system 200 to help flow anolyte 246to and from anodic half cell 242. In some examples, pump 258 may bedisposed between anolyte source tank 250 and anolyte inlet 242 andconnected therebetween by conduits 256. In other examples, pump 258 maybe disposed between anolyte source tank 250 and anolyte outlet 234 andconnected therebetween by conduits 256. Therefore, in one specificexample, anolyte 246 may circulate within the anodic side 240 of flowbattery system 200 by flowing from anolyte source tank 250, throughconduits 256, through anolyte inlet 252, along anolyte pathway 253within anodic half cell 242, through anolyte outlet 254, throughconduits 256, and back to anolyte source tank 250. Anolyte 246 may havea forward flow (as depicted in FIGS. 2A, 2C, 2E, and 2G-2I with arrows)or may have a reverse flow during different time periods of thecharge/discharge cycles. The fluid velocity of anolyte 246 may be withina range from about 1 cm/sec to about 25 cm/sec, such as from about 2cm/sec to about 15 cm/sec, for example, about 5 cm/sec or about 10cm/sec.

In some embodiments, anolyte 246 may be a solid anolyte, and therefore,certain portions or elements of the anodic side 240, as depicted in FIG.2A, may be optional or absent portions or derivatives thereof, such asanolyte inlet 252, anolyte outlet 254, anolyte source tank 250, conduits256, and/or pump 258. A solid anolyte 246 may have a thickness within arange from about 0.2 mm to about 5 mm, or from about 0.5 mm to about 3mm, such as about 1 mm or about 2 mm.

In some examples, anolyte 246 may be an Fe(II)/Fe(III) electrolyte, suchas a ferro/ferricyanide electrolyte. Anolyte 246 may initially contain aferrocyanide compound which is oxidized to the respective ferricyanidecompound during a recharge of the battery or cell. Several exemplaryferrocyanide compounds that may be contained within the anolyte 246include sodium ferrocyanide, such as tetrasodium hexacyanoferratedecahydrate (Na₄Fe(CN)₆.10H₂O), also known as yellow prussiate of soda,available from ScienceLab.com, as well as potassium ferrocyanide, suchas tetrapotassium hexacyanoferrate decahydrate (K₄Fe(CN)₆.10H₂O).Anolyte 246 generally contains hydroxide and additional hydroxidesolution may be added to the anolyte 246 during the charge/dischargecycles in order to maintain a desired hydroxide concentration. Theaqueous hydroxide solution generally contains sodium hydroxide,potassium hydroxide, or mixtures thereof.

Anode 244, such as a redox electrode, may have a variety of geometries,such as a flat planar anode, a planar anode, a plate anode, acylindrical anode, or the like. Anode 244 may be may be solid, or mayhave a high surface area configuration, such as being porous, expandedor foamed. Usually, anode 244 contains nickel, iron, chromium, steel,stainless steel, graphite, alloys thereof, derivatives thereof, orcombinations thereof. Anode 244 may be plated or coated with anothermaterial or metal, such as a graphite anode coated or plated with nickelor a nickel alloy. In one example, anode 244 is a planar electrode andcontains stainless steel. In another example, anode 244 is porous,foamed, or expanded and contains nickel or a nickel alloy, such asnickel foam, expanded nickel, perforated nickel, nickel wire, or wovennickel wire. In another example, anode 244 contains graphite, such asporous graphite, graphite foam, nickel plated graphite foam, graphitefelt, nickel plated graphite felt, or derivatives thereof. In someembodiments, anode 244 may have a length within a range from about 5 cmto about 300 cm, such as from about 10 cm to about 50 cm, such as fromabout 20 cm to about 30 cm and may have a height within a range fromabout 5 cm to about 300 cm, such as from about 10 cm to about 50 cm,such as from about 20 cm to about 30 cm. Additionally, anode 244 mayhave a thickness within a range from about 0.5 mm to about 5 mm, such asfrom about 1 mm to about 3 mm.

Electrolyte membrane 210 is disposed between cathodic half cell 222 andanodic half cell 242 and in contact with both catholyte 226 and anolyte246. Electrolyte membrane 210 may be an exchange membrane, a separator,or the like which isolates catholyte 226 and anolyte 246. In manyembodiments, electrolyte membrane 210 is an ionic exchange membrane—suchas a cationic exchange membrane—which is semipermeable to some cations(e.g., Na+ or K+) which migrate through electrolyte membrane 210 betweenthe anolyte 246 and catholyte 226. Electrolyte membrane 210 may containor be made from an ionic resin and/or a polymeric, co-polymeric, oroligomeric material, such as polytetrafluoroethylene, polyvinyl,polystyrene, polyethylene, polypropylene, polyester, derivativesthereof, or combinations thereof. Generally, electrolyte membrane 210 isdurable and has high ionic conductivity and chemical stability. In oneexample, electrolyte membrane 210 contains a polymeric backbone of PTFE,such as NAFION® 112, 115, 117, and 424 membranes, which are commerciallyavailable from DuPont. In another example, electrolyte membrane 210contains a co-polymer of tetrafluoroethylene and a vinylene monomer,such as a XUS® membrane, which is commercially available from DowChemical Company. Electrolyte membrane 210 may have a thickness within arange from about 0.005 mm to about 0.5 mm. In some examples, electrolytemembrane 210 may have a thickness of about 0.015 mm. In an alternativeembodiment, electrolyte membrane 110 may be a separator, such as aribbed separator, formed from a polymeric material and precipitatedsilica, such that the internal structure is very porous, tortuous, andhydrophilic (e.g., hydrophilic porous plastic separator), which iscommercially available from the AMER-SIL company.

Cathodic contact 262 and anodic contact 264 may be coupled to orotherwise in electrical contact with for discharging or removing thestored power from flow battery cell 202 while in use, or alternatively,for charging or storing power to flow battery system 200. Each flowbattery cell 202 may be electrically connected (e.g., in parallel or inseries) by cathodic contacts 262 and anodic contacts 264 to form thedesirable circuit for flow battery system 200. In one example, theplurality of flow battery cells 202 may be electrically connected inseries in order to have constant amperage and increased voltage for flowbattery system 200. Alternatively, the plurality of flow battery cells202 may be electrically connected in parallel in order to have constantvoltage and increased amperage for flow battery system 200.

Flow battery system 200 is illustrated having just one flow battery cell202, however, flow battery system 200 often contains multiple cellssimilar to flow battery cell 202. The specific quantity of flow batterycells 202 may be determined based on the total capacity of each flowbattery cell 202 and the relative total desired energy capacity for theoverall flow battery system 200. A plurality of flow battery cells 202may be connected together for storing the total desired energy capacity.

FIGS. 3A-3F depict a flow battery cell 300 which may be incorporatedinto a flow battery system, such as flow battery systems 100, 200, 400,and 600 described in embodiments herein. Flow battery cell 300 containscathodic half cell 308 and anodic half cell 348 separated by electrolytemembrane 344. Electrolyte membrane 344 is disposed between membranesupport frames 340 and 342 and maintains the catholyte and the anolyteseparate from each other.

Cathodic half cell 308 contains electrode plate retainer 310 coupledwith screw plate frame 330 coupled with membrane support frame 340.Cathode 322 coupled with cathode support plate 320 are both disposedbetween electrode plate retainer 310 and screw plate frame 330. Cathodesupport plate 320 contains or is made of an electrically insulatingmaterial, such as, a polymeric or oligomeric material. Cathodic halfcell 308 may have one, two, or more catholyte inlets 332 and may haveone, two, or more catholyte outlets 334. Catholyte inlets 332 andcatholyte outlets 334 are coupled to membrane support frame 340 and arein fluid communication with the catholyte pathways extending through thecavity formed within cathodic half cell 308. Catholyte flows from thecatholyte inlet 332 to the catholyte outlet 334 along a catholytepathway while exposing cathode 322. A thermometer 382 is coupled withand passes through membrane support frame 340 and is in physical and/orthermal contact with the catholyte flowing through the catholyte pathwaywithin cathodic half cell 308. Cathodic half cell 308 optionallycontains catholyte reference electrodes 386, such as mercury oxideelectrodes, which are exposed to the catholyte.

In one embodiment, cathode 322 may be a plate, planar, or flat cathodewhich contains a material such as graphite or a metal, such as nickel,iron, chromium, stainless steel, zinc, cadmium, lead, mercury, alloysthereof, or combinations thereof. In other embodiments, the variouscathodes described in embodiments herein may be utilized as cathode 322,such as planar cathode 124 in combination with open block flow screen160, cathodic wires 228, cathodic wire assembly 500, slotted sheetcathode 660, or derivatives thereof.

Anodic half cell 348 contains electrode plate retainer 350 coupled withscrew plate frame 370 coupled with membrane support frame 342. Anode 362coupled with anode support plate 360 are both disposed between electrodeplate retainer 350 and screw plate frame 370. Anode support plate 360contains or is made of an electrically insulating material, such as, apolymeric or oligomeric material.

Anodic half cell 348 may have one, two, or more anolyte inlets 352 andmay have one, two, or more anolyte outlets 354. Anolyte inlets 352 andanolyte outlets 354 are coupled to membrane support frame 342 and are influid communication with the anolyte pathways extending through thecavity formed within anodic half cell 348. Anolyte flows from theanolyte inlet 352 to the anolyte outlet 354 along a catholyte pathwaywhile exposing anode 362. A thermometer 382 is coupled with and passesthrough membrane support frame 342 and is in physical and/or thermalcontact with the anolyte flowing through the anolyte pathway withinanodic half cell 348. Anodic half cell 348 optionally contains anolytereference electrodes 384, such as mercury oxide electrodes, which areexposed to the anolyte.

Anode 362, such as a redox electrode, may have a variety of geometries,such as a flat planar anode, a planar anode, a plate anode, acylindrical anode, or the like. Anode 362 may be may be solid, or mayhave a high surface area configuration, such as being porous, expandedor foamed. Usually, anode 362 contains nickel, iron, chromium, steel,stainless steel, graphite, alloys thereof, derivatives thereof, orcombinations thereof. Anode 362 may be plated or coated with anothermaterial or metal, such as a graphite anode coated or plated with nickelor a nickel alloy. In one example, anode 362 is a planar electrode andcontains stainless steel. In another example, anode 362 is porous,foamed, or expanded and contains nickel or a nickel alloy, such asnickel foam, expanded nickel, perforated nickel, nickel wire, or wovennickel wire. In another example, anode 362 contains graphite, such asporous graphite, graphite foam, nickel plated graphite foam, graphitefelt, nickel plated graphite felt, or derivatives thereof. In someembodiments, anode 362 may have a length within a range from about 5 cmto about 300 cm, such as from about 10 cm to about 50 cm, such as fromabout 20 cm to about 30 cm and may have a height within a range fromabout 5 cm to about 300 cm, such as from about 10 cm to about 50 cm,such as from about 20 cm to about 30 cm. Additionally, anode 362 mayhave a thickness within a range from about 0.5 mm to about 5 mm, such asfrom about 1 mm to about 3 mm.

Cathodic contact 372 is in electrical contact with cathode 332 andanodic contact 374 is in electrical contact with anode 362. In someembodiments, cathodic contact 372 may be directly attached to cathode332 and anodic contact 374 may be directly attached to anode 362.Alternatively, controllers, switches, electrical contacts, and/or othercircuitry may be coupled with and/or between cathodic contact 372 andcathode 332 or may be coupled with and/or between anodic contact 374 andanode 362. In some examples, cathodic contact 372 may pass through anopening in the middle of cathode support plate 320 and be in physicaland electrical contact with cathode 332. Similarly, anodic contact 374may pass through an opening in the middle of anode support plate 360 andbe in physical and electrical contact with anode 322.

In an alternative embodiment, a bipolar plate (not shown) may besubstituted for both cathodic contact 372 and anodic contact 374 anddisposed on any outside surface of each flow battery cell 300. Eachbipolar plate contains a cathodic contact which extends between theinside and outside of and in electrical contact with the cathodic halfcell 308 and also contains an anodic contact which extends between theinside and outside of and in electrical contact with the anodic halfcell 348. The bipolar plates may provide alternative configurations whenstacking or otherwise positioning a plurality of flow battery cells 300to form a flow battery system.

FIGS. 3A-3D illustrate handles attached to cathode support plate 320 andanode support plate 360. Handles 312 may be attached to the flow batterycell 300 at numerous positions wherein multiple flow battery cells 300may be stacked or otherwise efficiently positioned without beingobstructed by the handles 312. Optionally, the handles 312 may beremoved upon positioning flow battery cells 300 or simply omitted fromthe flow battery cell 300.

FIG. 4 depicts a flow battery system 400 containing a plurality of flowbattery cells 402 as described by another embodiment. Although flowbattery system 400 is illustrated with 10 flow battery cells, however,flow battery system 400 may contain a single flow battery cell 402 ormay contain any number of flow battery cells 402 dependent to desiredstorage capacity for electrical power. The particular number of flowbattery cells 402 may be determined based on the total capacity of eachflow battery cell 402 and the relative total desired energy capacity forthe overall flow battery system 400. In many embodiments, flow batterysystem 400 contains 2 or more flow battery cells 402, such as 3, 4, 6,8, 10, 12, 20, 24, 30, 40, 50, 80, 100, or more flow battery cells 402.

In other embodiments, one or multiple flow battery cells 402 may bereplaced with one or multiple flow battery cells 102, 202, 300, 602, ormixtures thereof, as described by embodiments herein. Therefore, flowbattery system 400 may contain a plurality of flow battery cells whichincludes any number of flow battery cells 102, 202, 300, 402, or 602incorporated into a single system. In another embodiment, flow batterycells 102, 202, 300, 402, and/or 602 may be positioned and/or rotated tobe disposed in a variety of positions to assembly flow battery system400, flow battery systems 100, 200, or 600 described herein, as well asother flow battery systems. For example, flow battery cells 102 (FIGS.1A-1B), 202 (FIGS. 2A-2I), and 602 (FIGS. 6A-6B) are depicted as havinghorizontal flow paths for the catholyte and the anolyte. The horizontalflow paths extend between the respective inlets and outlets within eachflow battery cell at a horizontal direction relative to gravity, such asbeing perpendicular or substantially perpendicular to the gravitationalforce. Alternatively, flow battery cells 300 (FIGS. 3A-3F) and 402 (FIG.4) are depicted as having vertical flow paths for the catholyte and theanolyte. The vertical flow paths extend between the respective inletsand outlets within each flow battery cell at a vertical directionrelative to gravity, such as being parallel or substantially parallelwith the gravitational force. However, flow battery cells 102, 202, 300,402, and/or 602 are not limited at being positioned to have horizontalor vertical flow paths for the electrolytes and may be positioned and/orrotated at any angle.

Each of the flow battery cells 402 is in fluid communication withcatholyte source tank 430 and anolyte source tank 450 by a conduitsystem. In some embodiments, the catholyte circulates between each ofthe cathodic half cells within flow battery cells 402 and catholytesource tank 430 by conduits 436, similar as the anolyte circulatesbetween each of the anodic half cells within flow battery cells 402 andanolyte source tank 450 by conduits 456. Conduits 436 extend betweencatholyte source tank 430 to catholyte inlet 432 and from catholyteoutlet 434 to catholyte source tank 430, similar as conduits 456 extendbetween anolyte source tank 450 to anolyte inlet 452 and from anolyteoutlet 454 to anolyte source tank 450. Pumps 438 and 458 may beincorporated within flow battery system 400 to help flow the catholyteand anolyte to and from the respective half cell with each flow batterycell 402.

The catholyte may have a forward flow (as depicted in FIG. 4 witharrows) through conduits 436 or may have a reverse flow during differenttime periods of the charge/discharge cycles. The fluid velocity of thecatholyte may be within a range from about 1 cm/sec to about 25 cm/sec,such as from about 2 cm/sec to about 15 cm/sec, for example, about 5cm/sec or about 10 cm/sec. Therefore, in one specific example, thecatholyte may circulate within the cathodic side of flow battery system400 by flowing from catholyte source tank 430, through conduits 436,through catholyte inlet 432 and into the cathodic half cell, out of thecathodic half cell by catholyte outlet 434, through conduits 436, andback to catholyte source tank 430.

The anolyte may have a forward flow (as depicted in FIG. 4 with arrows)through conduits 456 or may have a reverse flow during different timeperiods of the charge/discharge cycles. The fluid velocity of theanolyte may be within a range from about 1 cm/sec to about 25 cm/sec,such as from about 2 cm/sec to about 15 cm/sec, for example, about 5cm/sec or about 10 cm/sec. In another specific example, the anolyte maycirculate within the anodic side of flow battery system 400 by flowingfrom anolyte source tank 450, through conduits 456, through anolyteinlet 452 and into the anodic half cell, out of the anodic half cell byanolyte outlet 454, through conduits 456, and back to anolyte sourcetank 450.

Each of the flow battery cells 402 may have a cathodic contact 424 andan anodic contact 444. Cathodic contact 424 may be disposed on flowbattery cell 402 and extends between the inside and outside of eachcathodic half cell. Similarly, anodic contact 444 may be disposed onflow battery cell 402 and extends between the inside and outside of eachanodic half cell.

Cathodic contact 424 and anodic contact 444 may be coupled to orotherwise in electrical contact with for discharging or removing thestored power from flow battery cell 402 while in use, or alternatively,for charging or storing power to flow battery system 400. Each flowbattery cell 402 may be electrically connected (e.g., in parallel or inseries) by cathodic contacts 424 and anodic contacts 444 to form thedesirable circuit for flow battery system 400. As depicted in FIG. 4,the plurality of flow battery cells 402 may be electrically connected inseries in order to have constant amperage and increased voltage for flowbattery system 400. Alternatively, the plurality of flow battery cells402 may be electrically connected in parallel in order to have constantvoltage and increased amperage for flow battery system 400.

In an alternative embodiment, a bipolar plate (not shown) may besubstituted for both cathodic contact 424 and anodic contact 444 anddisposed on any outside surface of each flow battery cell 402. Eachbipolar plate contains a cathodic contact which extends between theinside and outside of and in electrical contact with the cathodic halfcell and also contains an anodic contact which extends between theinside and outside of and in electrical contact with the anodic halfcell. The bipolar plates may provide alternative configurations whenstacking or otherwise positioning a plurality of flow battery cells 402to form a flow battery system 400.

FIGS. 5A-5C depict cathodic wire assembly 500, which may be incorporatedinto the flow battery systems as described herein, such as flow batterysystem 200. Cathodic wire assembly 500 contains frame 502 having anopening 504 and a plurality of cathodic wires 530 extending acrossopening 504. Frame 502 and opening 504 are both illustrated withrectangular or square geometries, but other geometries may independentlybe utilized for frame 502 and opening 504. Frame 502 contains frame body506 encompassed by a protective shell 522. Frame body 506 may contain orbe formed from a plastic material, such as a molded plastic, which maybe a single piece of plastic material or multiple pieces adheredtogether. Protective shell 522 may contain or be formed from anelastomeric material or an oligomeric material, which may be a singlepiece of material or multiple pieces. Frame body 506 and protectiveshell may contain or be made from exemplary materials such aspolyethylene, polypropylene, natural polypropylene (NPP), polyphenyleneoxide (PPO), polyphenylene sulfide (PPS), polyvinyl chloride (PVC),polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP),perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), as well as otherfluoropolymers, derivatives thereof, or combinations thereof. Generally,natural polypropylene (NPP) is polypropylene containing no pigment orsubstantially no pigment and/or being unfilled or substantiallyunfilled.

Raised seal 524 may be disposed on frame 502 and used to form a tightfit or enclosure when cathodic wire assembly 500 is incorporated into aflow battery system. Raised seal 524 may be an o-ring or seal placednear the perimeter frame 502 or may be formed as an intimate portion ofprotective shell 522.

The plurality of cathodic wires 530 extends between sides 518 and 520 offrame 502 and across opening 504. FIG. 5A illustrates a single row ofcathodic wires 530 containing 10 wires. In other embodiments, cathodicwire assembly 500 may contain 2 or more rows of cathodic wires 530 andmay have any number of wires within each row. In some embodiments,cathodic wires 530 may be strung in a loop around a first headed pin 534positioned on side 518 and a second headed pin 534 is positioned on side520. Therefore, a single piece of wire may be utilized to form twocathodic wires 530 in some embodiments, while other embodiments providethat a single piece of wire may be utilized to form all of the cathodicwires 530. Alternatively, each cathodic wire 530 may be a single pieceof wire attached to a headed pin 534 on each side of the wire. In oneconfiguration, a first row of headed pins 534 extends along side 518 ofthe front side 510 of frame body 506 and a second row of headed pins 534extends along side 520 of the front side 510 of frame body 506, asillustrated in FIGS. 5B-5C. In another configuration, a first row ofheaded pins 534 extends along side 518 of the back side 512 of framebody 506 and a second row of headed pins 534 extends along side 520 ofthe back side 512 of frame body 506, as illustrated in FIG. 5C.

In one embodiment, both rows of headed pins 534 on the front side 510 orback side 512 extend parallel or substantially parallel to each otherand have the same amount of headed pins 534, such that each headed pin534 in the first row is paired up with each consecutive headed pin 534in the second row. Either one wire extends between each pair of headedpins 534 or a looped wire is strung around each pair of headed pins 534to provide the cathodic wires 530. In another embodiment, two rows ofheaded pins 534 extend along side 518—one row on each of the front side510 and the back side 512 and two rows of headed pins 534 extend alongside 520—one row on each of the front side 510 and the back side 512, asillustrated in FIG. 5C. The cathodic wires 530 strung between the tworows of headed pins 534 extending along the front side 510 form a firstarray of cathodic wires 530 and the cathodic wires 530 strung betweenthe two rows of headed pins 534 extending along the back side 512 form asecond array of cathodic wires 530.

In one embodiment, the two rows or arrays of cathodic wires 530 arealigned relative to each other, as shown in FIG. 5C. Alternatively, inanother embodiment not shown, the two rows or arrays of cathodic wires530 are staggered, off-set, or otherwise unaligned relative to eachother. A pair of staggered rows of cathodic wires 530 may be formed bystaggering or off-setting the position of the headed pins 534 on thefront side 510 relative to the position of the headed pins 534 on theback side 512.

Cathodic wires 530 may independently contain a metal, such as cadmium,iron, steel, stainless steel, nickel, chromium, silver, gold, platinum,palladium, platings thereof, alloys thereof, derivatives thereof, orcombinations thereof. In some examples, cathodic wires 530 containcadmium or a cadmium alloy. Cathodic wires 530 may be a solid cadmiumwire, a solid cadmium alloy wire, a cadmium plated metallic wire, suchas a steel or stainless steel wire plated with cadmium or a cadmiumalloy. In many embodiments, the length of cathodic wires 530 may bewithin a range from about 10 cm to about 50 cm, such as from about 20 cmto about 30 cm. Cathodic wires 530 may have a diameter within a rangefrom about 0.001 inch to about 0.1 inch, or such as, from about 0.005inch to about 0.05 inch, or such as, from about 0.01 inch to about 0.04inch, or such as, from about 0.02 inch to about 0.03 inch, for example,about 0.012 inch, 0.024 inch or 0.036 inch.

Contact bar 540 is coupled with and in electrical contact with each ofthe cathodic wires 530, as depicted in FIG. 5C. Contact bar 540 isconfigured to be in electrical contact with the cathodic contact of theflow battery cell. FIG. 5C illustrates contact bar 540 extending fromthe top 514 of frame 502, however, contact bar 540 may extend from thebottom 516, sides 518 and 520, front 510, and/or back 512 of frame 502in order to make electrical contact with the cathodic contact of theflow battery cell. Contact bar 540 may be disposed within frame body 506and/or between frame body 506 and protective shell 522. Contact bar 540contains a conductive material, such as a metal. Contact bar 540 may bea wire, a plate, a bar, a ribbon, or similar contact/conductive surface.Contact bar 540 may contain iron, steel, stainless steel, copper,nickel, chromium, silver, gold, aluminum, cadmium, platinum, palladium,platings thereof, alloys thereof, derivatives thereof, or combinationsthereof.

FIGS. 6A-6B depict a flow battery system 600 containing a flow batterycell 602 which has a cathodic half cell 622 and an anodic half cell 642separated by electrolyte membrane 610, as described in multipleembodiments herein. Cathodic half cell 622 is on the cathodic side 620of flow battery system 600 and has multiple slotted sheet cathodes 660,which extend through and are in fluid communication with catholyte 626in catholyte pathway 633. The slotted sheet cathodes 660 extendperpendicular or substantially perpendicular to catholyte pathway 633and each of the slotted sheet cathodes 660 extends parallel orsubstantially parallel to each other. Each slotted sheet cathode 660contains a plurality of cathodic strips 662 separated by slots 664, asdepicted in FIG. 6C.

FIGS. 6A-6B illustrate flow battery cell 602 containing two slottedsheet cathodes 660. However, in other configurations, flow battery cell602 may have only one slotted sheet cathode 660, or may have multipleslotted sheet cathodes 660, such as 2, 3, 4, 5, 6, or more, such as 10,20, or more. The slotted sheet cathodes 660 are disposed within thecathodic half cell 622 on the cathodic side 620 of flow battery system600.

As depicted by FIG. 6B from the perspective of viewing across the widthof the cathodic half cell 622 from the electrolyte membrane 610—the twoslotted sheet cathodes 660 are aligned with each other such that theslotted sheet cathode 660 closest to the electrolyte membrane 610completely overshadows the slotted sheet cathode 660 furthest from theelectrolyte membrane 610. The cathodic strips 662 within the slottedsheet cathode 660 closest to the electrolyte membrane 610 form a firstarray of cathodic strips 662 and the cathodic strips 662 within theslotted sheet cathode 660 furthest from the electrolyte membrane 610form a second array of cathodic strips 662.

Alternatively, in another embodiment not shown, the two slotted sheetcathodes 660 are staggered with each other such that the two slottedsheet cathodes 660 are unaligned relative to each other from theperspective of viewing across the width of the cathodic half cell 622from the electrolyte membrane 610. Therefore, each row or array ofcathodic strips 662 is also staggered relative to each other.

Catholyte 626 may be flowed into catholyte inlet 632 which is disposedon cathodic half cell 622, along catholyte pathway 633, and out fromcatholyte outlet 634 disposed on cathodic half cell 622. Catholytepathway 633 extends between catholyte inlet 632 and catholyte outlet 634within cathodic half cell 622. In most embodiments, catholyte 626 is aliquid electrolyte, such as an aqueous based electrolyte. In someexamples, catholyte 626 may be a zinc electrolyte. In one example, thecatholyte for a zinc/ferrocyanide battery is alkaline. The catholyte maycontain a hydroxide concentration within a range from about 1 N to about7 N, such as from about 2 N to about 5 N. The hydroxide may be sodiumhydroxide or potassium hydroxide and may be saturated with zincate. Insome examples, the catholyte 626 may be saturated or supersaturated,such that zincate precipitates in the bath forming solid suspensions.

Outside of flow battery cell 602, catholyte 626 circulates betweencathodic half cell 622 and catholyte source tank 630 by conduits 636.Conduits 636 extend between catholyte source tank 630 to catholyte inlet632 and from catholyte outlet 634 to catholyte source tank 630. One ormultiple pumps, such as pump 638, may be incorporated within flowbattery system 600 to help flow catholyte 626 to and from cathodic halfcell 622. In some examples, pump 638 may be disposed between catholytesource tank 630 and catholyte inlet 632 and connected therebetween byconduits 636. In other examples, pump 638 may be disposed betweencatholyte source tank 630 and catholyte outlet 634 and connectedtherebetween by conduits 636. Therefore, in one specific example,catholyte 626 may circulate within the cathodic side 620 of flow batterysystem 600 by flowing from catholyte source tank 630, through conduits636, through catholyte inlet 632, along catholyte pathway 633, acrosscathodic strips 662 and through slots 664 of slotted sheet cathode 660within cathodic half cell 622, through catholyte outlet 634, throughconduits 636, and back to catholyte source tank 630. Catholyte 626 mayhave a forward flow (as depicted in FIG. 6A with arrows) or may have areverse flow during different time periods of the charge/dischargecycles. The fluid velocity of catholyte 626 may be within a range fromabout 1 cm/sec to about 25 cm/sec, such as from about 2 cm/sec to about15 cm/sec, for example, about 5 cm/sec or about 10 cm/sec.

In another embodiment, the flow battery cell 602 is configured toimprove metal plating uniformity due to the dimensions of the cathodichalf cell 622 which provides an increased velocity for a givenvolumetric fluid velocity of the catholyte 626 along catholyte pathway633. In many configurations, the cathodic half cell 622 may have thelength greater than the height along the catholyte pathway 633 and theheight greater than the width along the catholyte pathway 633. Thisincreased volumetric flow rate in turn provides minimal depletion ofbulk level of chemistry across the length of catholyte pathway 633. Theconcentration of the catholyte 626 stays substantially constant whilemetal is plating on the cathodic strips 662. Therefore, flow batterycell 602 has a longer length along the flow direction of catholytepathway 633 than a width, which results in the highest fluid velocitiesfor a given volumetric flow rate.

The width of cathodic half cell 622 across catholyte pathway 633 (e.g.,normal the length and height) may be within a range from about 1 mm toabout 20 mm, such as, from about 5 mm to about 15 mm, for example, about10 mm. The length of cathodic half cell 622 along catholyte pathway 633(e.g., between catholyte inlet 632 and catholyte outlet 634) may bewithin a range from about 5 cm to about 300 cm, such as, from about 20cm to about 200 cm, such as, from about 50 cm to about 100 cm. Theheight of cathodic half cell 622 along catholyte pathway 633 (e.g.,between bottom and top portions 612 and 614) may be within a range fromabout 5 cm to about 300 cm, such as, from about 20 cm to about 200 cm,such as, from about 50 cm to about 100 cm. In one example, cathodic halfcell 622 may have a length of about 200 cm, a height of about 10 cm, anda width of about 10 mm. In another example, cathodic half cell 622 mayhave a length of about 100 cm, a height of about 20 cm, and a width ofabout 10 mm.

FIG. 6C depicts a slotted sheet cathode 660 which contains cathodicstrips 662 separated by slots 664 and extending between the upperportion 666 and the lower portion 668 of slotted sheet cathode 660.Slotted sheet cathode 660 may contain or be formed from a metallic sheet(e.g., a stainless steel sheet) in which slots 664 have been disposed,stamped, cut, or otherwise formed there through or within. Each slottedsheet cathode 660 and cathodic strips 662 may contain or be formed froma metal such as iron, steel, stainless steel, cadmium, chromium, nickel,alloys thereof, or combinations thereof. In some examples, slotted sheetcathode 660 may be formed from a cadmium plated stainless steel sheet.

In many embodiments, the height of the slotted sheet cathode 660 may bethe same, substantially the same, or shorter than the length ofcatholyte pathway 633 or the length of cathodic half cell 622.Therefore, the height of the slotted sheet cathode 660 may be within arange from about 5 cm to about 300 cm, such as, from about 20 cm toabout 200 cm, such as, from about 50 cm to about 100 cm. Also, theslotted sheet cathode 660 may have a thickness within a range from about0.005 inch to about 0.1 inch, such as, from about 0.01 inch to about0.05 inch, for example, about 0.02 inch.

The length of the cathodic strips 662 may be the same, substantially thesame, or shorter than the height of the cathodic half cell 622. Eachcathodic strip 662 and/or slots 664 may have a length within a rangefrom about 5 cm (about 1.97 inches) to about 300 cm (about 118.11inches). In some examples, each cathodic strip 662 and/or slots 664 mayhave a length within a range from about 20 cm (about 7.87 inches) toabout 200 cm (about 78.74 inches), or from about 50 cm (about 19.69inches) to about 100 cm (about 39.37 inches). In other examples, eachcathodic strip 662 and/or slots 664 may have a length within a rangefrom about 5 cm (about 1.97 inches) to about 50 cm (about 19.69 inches),such as from about 20 cm (about 7.87 inches) to about 30 cm (about 11.81inches). Each cathodic strip 662 and/or slot 664 may have a width withina range from about 0.005 inch to about 0.1 inch, such as, from about0.01 inch to about 0.05 inch, for example, about 0.02 inch. Eachcathodic strip 662 and/or slot 664 may have a thickness within a rangefrom about 0.005 inch to about 0.1 inch, such as, from about 0.01 inchto about 0.05 inch, for example, about 0.02 inch.

FIG. 6C depicts cathodic strips 662 aligned in straight and parallelrows as viewed across the front surface of slotted sheet cathode 660.However, in alternative embodiments, the plurality of cathodic strips662 may be unaligned, not parallel, and/or asymmetrical as viewed acrossthe front surface of slotted sheet cathode 660. The cathodic strips 662and/or each of the slots 664 may independently have various geometriesor shapes. In some examples, cathodic strips 662 are formed during oneor more processes which may include cutting, stamping, punching, orforging the cathodic strips 662 in order to have a particular two orthree dimensional geometry. Each of the cathodic strips 662 and/or eachof the slots 664 may independently have a geometry or shape selectedfrom rectangle, square, circle, oval, eclipse, curve, round, derivativesthereof, as well as other geometries.

In some embodiments, the slotted sheet cathode 660 may be furtherprocessed to obtain a particular shape or geometry and/or to provide aparticular finished surface. For example, the slotted sheet cathode 660may be processed to round or smooth the edges of the cathodic strips662. In some examples, surfaces of the slotted sheet cathode660—including the edges of the cathodic strips 662 which extend alongthe length each cathodic strip 662—may be ground, filed, bent, rounded,sand-blasted, chemically-etched, heat-treated, plasma-treated, polished,or processed by other techniques in order to prepare smooth or roundededges or other desirable surfaces on the slotted sheet cathode 660.

In one example, slotted sheet cathode 660 is formed from a metallicsheet in which slots 664 of a rectangular geometry have been stamped orotherwise formed through the metallic sheet. The metallic sheet may havea thickness of about 0.02 inch—therefore—the cathodic strips 662 havethe same corresponding thickness of about 0.02 inch. The slots 664 maybe stamped out having a width of about 0.02 inch and are spaced apart byabout 0.02 inch—therefore—the cathodic strips 662 have the samecorresponding width of about 0.02 inch. Also, the slots 664 may bestamped out having a length of about 10 inches—therefore—the cathodicstrips 662 have the same corresponding length of about 10 inches.

FIG. 6A depicts contact bar 629 coupled to and in electrical contactwith each of the slotted sheet cathodes 660. One contact bar 629 isdepicted in FIG. 6A, however, numerous contact bars may be used toindividually control each cathodic strip 662 or an array of cathodicstrips 662. In many embodiments, contact bar 629 may be in electricalcontact with cathodic contact 628 by a controller and/or a set ofswitches (not shown). The controller and/or the set of switches may becoupled between and in electrical communication to the cathodic contact628 and the contact bar 629 or multiple contact bars. The controllerand/or the set of switches may be used to independently control byelectrically connecting/disconnecting each of the slotted sheet cathodes660—and therefore each row of the cathodic strips 662 contained withineach slotted sheet cathode 660—to the cathodic contact 628. In someconfigurations, the controller and/or the set of switches may be used toindependently charge and/or discharge each slotted sheet cathode 660.Once in electrical contact with cathodic contact 628, the cathodicstrips 662 become energized cathodes which are capable of beingplated/deplated during charge/discharge cycles.

In one embodiment, the controller is utilized to sequentially chargeand/or discharge each of the slotted sheet cathodes 660. In someexamples, cathodic half cell 622 may contain two arrays of slotted sheetcathodes 660, such that the first array contains energized slotted sheetcathodes and the second array contains non-energized slotted sheetcathodes. The first and second arrays may each have 1, 2, 3, 4, or moreslotted sheet cathodes 660. In one specific example, cathodic half cell622 contains a first array of two energized slotted sheet cathodes 660and a second array of two non-energized slotted sheet cathodes 660.

Contact bar 629 may be disposed inside or outside the cathodic half cell622, or within any of the surrounding walls or surfaces of cathodic halfcell 622, such as the bottom portion 612, the top portion 614, and/orthe sides 616 of cathodic half cell 622. Contact bar 629 may also extendalong at any length, width, and/or height of the cathodic half cell 622.In some embodiments, contact bar 629 may be disposed within the topportion 614 of cathodic half cell 622, as depicted in FIG. 6B. In otherembodiments, contact bar 629 may be disposed outside of the surroundingwalls or surfaces of cathodic half cell 622. For example, contact bar629 or a contact junction thereof may protrude through the bottomportion 612, the top portion 614, and/or the sides 616 of cathodic halfcell 622 to be physically and electrically coupled with each of thecathodic strips 662. Alternatively, each of the cathodic strips 662 mayprotrude through the bottom portion 612, the top portion 614, and/or thesides 616 of cathodic half cell 622 to be physically and electricallycoupled with contact bar 629. Contact bar 629 contains a conductivematerial, such as a metal. Contact bar 629 may be a wire, a plate, abar, a ribbon, or similar contact/conductive surface. Contact bar 629may contain iron, steel, stainless steel, copper, nickel, chromium,silver, gold, aluminum, cadmium, platinum, palladium, platings orcoatings thereof, alloys thereof, derivatives thereof, or combinationsthereof.

FIG. 6A depicts cathodic half cell 622 containing two slotted sheetcathodes 660 which are spaced apart with only catholyte 626 flowingbetween each slotted sheet cathodes 660. In an alternative embodiment,not shown, cathodic half cell 622 contains a plurality of slotted sheetcathodes 660 which are separated by thin electrically insulating sheetsdisposed between the slotted sheet cathodes 660. The electrically thininsulating sheets prevent neighboring slotted sheet cathodes 660 fromelectrically contacting each other when conducting sequentialcharge/discharge cycles.

Anodic half cell 642 is on the anodic side 640 of flow battery system600 and contains anode 644, which may be in fluid and/or conductivecommunication with anolyte 646. Anolyte 646 may be a liquid electrolyte,such as an aqueous based electrolyte or a solid electrolyte. Inembodiments when anolyte 646 is a liquid anolyte, anolyte 646 flows intoanolyte inlet 652 disposed on anodic half cell 642, along anolytepathway 653, and out from anolyte outlet 644 disposed on anodic halfcell 642. Anolyte pathway 653 extends between anolyte inlet 652 andanolyte outlet 654, as well as between anode 644 and electrolytemembrane 610 within anodic half cell 642.

Outside of flow battery cell 602, in embodiments when anolyte 646 is aliquid anolyte, anolyte 646 circulates between anodic half cell 642 andanolyte source tank 650 by conduits 656. Conduits 656 extend betweenanolyte source tank 650 to anolyte inlet 652 and from anolyte outlet 654to anolyte source tank 650. One or multiple pumps, such as pump 658, maybe incorporated within flow battery system 600 to help flow anolyte 646to and from anodic half cell 642. In some examples, pump 658 may bedisposed between anolyte source tank 650 and anolyte inlet 642 andconnected therebetween by conduits 656. In other examples, pump 658 maybe disposed between anolyte source tank 650 and anolyte outlet 634 andconnected therebetween by conduits 656. Therefore, in one specificexample, anolyte 646 may circulate within the anodic side 640 of flowbattery system 600 by flowing from anolyte source tank 650, throughconduits 656, through anolyte inlet 652, along anolyte pathway 653within anodic half cell 642, through anolyte outlet 654, throughconduits 656, and back to anolyte source tank 650. Anolyte 646 may havea forward flow (as depicted in FIG. 6A with arrows) or may have areverse flow during different time periods of the charge/dischargecycles. The fluid velocity of anolyte 646 may be within a range fromabout 1 cm/sec to about 25 cm/sec, such as from about 2 cm/sec to about15 cm/sec, for example, about 5 cm/sec or about 10 cm/sec.

In some embodiments, anolyte 646 may be a solid anolyte, and therefore,certain portions or elements of the anodic side 640, as depicted in FIG.6A, may be optional or absent portions or derivatives thereof, such asanolyte inlet 652, anolyte outlet 654, anolyte source tank 650, conduits656, and/or pump 658. A solid anolyte 246 may have a thickness within arange from about 0.2 mm to about 5 mm, or from about 0.5 mm to about 3mm, such as about 1 mm or about 2 mm.

In some examples, anolyte 646 may be an Fe(II)/Fe(III) electrolyte, suchas a ferro/ferricyanide electrolyte. Anolyte 646 may initially contain aferrocyanide compound which is oxidized to the respective ferricyanidecompound during a recharge of the battery or cell. Several exemplaryferrocyanide compounds that may be contained within the anolyte 646include sodium ferrocyanide, such as tetrasodium hexacyanoferratedecahydrate (Na₄Fe(CN)₆.10H₂O), also known as yellow prussiate of soda,available from ScienceLab.com, as well as potassium ferrocyanide, suchas tetrapotassium hexacyanoferrate decahydrate (K₄Fe(CN)₆.10H₂O).Anolyte 646 generally contains hydroxide and additional hydroxidesolution may be added to the anolyte 646 during the charge/dischargecycles in order to maintain a desired hydroxide concentration. Theaqueous hydroxide solution generally contains sodium hydroxide,potassium hydroxide, or mixtures thereof.

Anode 644, such as a redox electrode, may have a variety of geometries,such as a flat planar anode, a planar anode, a plate anode, acylindrical anode, or the like. Anode 644 may be may be solid, or mayhave a high surface area configuration, such as being porous, expandedor foamed. Usually, anode 644 contains nickel, iron, chromium, steel,stainless steel, graphite, alloys thereof, derivatives thereof, orcombinations thereof. Anode 644 may be plated or coated with anothermaterial or metal, such as a graphite anode coated or plated with nickelor a nickel alloy. In one example, anode 644 is a planar electrode andcontains stainless steel. In another example, anode 644 is porous,foamed, or expanded and contains nickel or a nickel alloy, such asnickel foam, expanded nickel, perforated nickel, nickel wire, or wovennickel wire. In another example, anode 644 contains graphite, such asporous graphite, graphite foam, nickel plated graphite foam, graphitefelt, nickel plated graphite felt, or derivatives thereof. In someembodiments, anode 644 may have a length within a range from about 5 cmto about 300 cm, such as from about 10 cm to about 50 cm, such as fromabout 20 cm to about 30 cm and may have a height within a range fromabout 5 cm to about 300 cm, such as from about 10 cm to about 50 cm,such as from about 20 cm to about 30 cm. Additionally, anode 644 mayhave a thickness within a range from about 0.5 mm to about 5 mm, such asfrom about 1 mm to about 3 mm.

Electrolyte membrane 610 is disposed between cathodic half cell 622 andanodic half cell 642 and in contact with both catholyte 626 and anolyte646. Electrolyte membrane 610 may be an exchange membrane, a separator,or the like which isolates catholyte 626 and anolyte 646. In manyembodiments, electrolyte membrane 610 is an ionic exchange membrane—suchas a cationic exchange membrane—which is semipermeable to some cations(e.g., Na+ or K+) which migrate through electrolyte membrane 610 betweenthe anolyte 646 and catholyte 626. Electrolyte membrane 610 may containor be made from an ionic resin and/or a polymeric, co-polymeric, oroligomeric material, such as polytetrafluoroethylene, polyvinyl,polystyrene, polyethylene, polypropylene, polyester, derivativesthereof, or combinations thereof. Generally, electrolyte membrane 610 isdurable and has high ionic conductivity and chemical stability. In oneexample, electrolyte membrane 610 contains a polymeric backbone of PTFE,such as NAFION® 112, 115, 117, and 424 membranes, which are commerciallyavailable from DuPont. In another example, electrolyte membrane 610contains a co-polymer of tetrafluoroethylene and a vinylene monomer,such as a XUS® membrane, which is commercially available from DowChemical Company. Electrolyte membrane 610 may have a thickness within arange from about 0.005 mm to about 0.5 mm. In some examples, electrolytemembrane 610 may have a thickness of about 0.015 mm. In an alternativeembodiment, electrolyte membrane 110 may be a separator, such as aribbed separator, formed from a polymeric material and precipitatedsilica, such that the internal structure is very porous, tortuous, andhydrophilic (e.g., hydrophilic porous plastic separator), which iscommercially available from the AMER-SIL company.

Although flow battery system 600 is illustrated having just one flowbattery cell 602, however, flow battery system 600 often containsmultiple cells similar to flow battery cell 602. The specific quantityof flow battery cells 602 may be determined based on the total capacityof each flow battery cell 602 and the relative total desired energycapacity for the overall flow battery system 600. A plurality of flowbattery cells 602 may be connected together for storing the totaldesired energy capacity.

Cathodic contact 628 and anodic contact 648 may be coupled to orotherwise in electrical contact with for discharging or removing thestored power from flow battery cell 602 while in use, or alternatively,for charging or storing power to flow battery system 600. Each flowbattery cell 602 may be electrically connected (e.g., in parallel or inseries) by cathodic contacts 628 and anodic contacts 648 to form thedesirable circuit for flow battery system 600. In one example, theplurality of flow battery cells 602 may be electrically connected inseries in order to have constant amperage and increased voltage for flowbattery system 600. Alternatively, the plurality of flow battery cells602 may be electrically connected in parallel in order to have constantvoltage and increased amperage for flow battery system 600.

While the foregoing is directed to embodiments of the invention, otherand further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. A flow battery cell, comprising: a cathodichalf cell comprising a catholyte, a catholyte inlet, a catholyte outlet,a catholyte pathway extending between the catholyte inlet and outlet andwithin the cathodic half cell, and a cathode comprising a plurality ofcathodic wires extending perpendicular or substantially perpendicular toand within the catholyte pathway and in contact with the catholyte,wherein each of the cathodic wires extends parallel or substantiallyparallel to each other; an anodic half cell comprising an anode inconductive contact with an anolyte; an electrolyte membrane disposedbetween the cathodic half cell and the anodic half cell and in contactwith the catholyte and anolyte; and a cathodic contact electricallyconnected with the cathode and disposed outside of the cathodic halfcell.
 2. The flow battery cell of claim 1, wherein the cathodic wirescomprise cadmium or a cadmium alloy.
 3. The flow battery cell of claim2, wherein the cathodic wires comprises wires selected from the groupconsisting of solid cadmium wires, stainless steel wires plated orcoated with cadmium or a cadmium alloy, metallic wires plated or coatedwith cadmium or a cadmium alloy, derivatives thereof, and combinationsthereof.
 4. The flow battery cell of claim 2, wherein the cathodic wireshave a diameter within a range from about 0.01 inch to about 0.04 inchand a length within a range from about 5 cm to about 300 cm.
 5. The flowbattery cell of claim 1, further comprising an anodic contactelectrically connected with the anode and disposed outside of the anodichalf cell, and the anode comprises iron, nickel, chromium, steel,stainless steel, alloys thereof, or combinations thereof.
 6. The flowbattery cell of claim 1, wherein the electrolyte membrane comprises apolymeric material and has a thickness within a range from about 0.005mm to about 0.5 mm.
 7. The flow battery cell of claim 1, wherein theplurality of cathodic wires comprises at least one row of cathodicwires, the at least one row extends along the catholyte pathway, thecathodic wires are spaced a predetermined distance from each otherwithin the row, and the predetermined distance is equal to orsubstantially equal to the circumference of the individual cathodicwire.
 8. The flow battery cell of claim 1, wherein the plurality ofcathodic wires comprises at least two arrays of cathodic wires, eacharray comprises at least one row of cathodic wires, and the rows extendalong the catholyte pathway.
 9. The flow battery cell of claim 8,wherein the plurality of cathodic wires comprises at least four rows ofcathodic wires.
 10. The flow battery cell of claim 9, wherein a firstarray of cathodic wires comprises energized cathodic wires and a secondarray of cathodic wires comprises non-energized cathodic wires.
 11. Theflow battery cell of claim 10, wherein the first array of cathodic wirescomprises at least two rows of energized cathodic wires and the secondarray of cathodic wires comprises at least two rows of non-energizedcathodic wires.
 12. The flow battery cell of claim 11, wherein the firstarray of cathodic wires is disposed between the second array of cathodicwires and the electrolyte membrane or wherein the second array ofcathodic wires is disposed between the first array of cathodic wires andthe electrolyte membrane.
 13. A flow battery system comprising two ormore flow battery cells of claim 1.